本篇内容介绍了“怎么理解Redis中的分布式锁”的有关知识，在实际案例的操作过程中，不少人都会遇到这样的困境，接下来就让小编带领大家学习一下如何处理这些情况吧！希望大家仔细阅读，能够学有所成！

大家项目中都会使用到分布式锁把，通常用来做数据的有序操作场景，比如一笔订单退款（如果可以退多次的情况）。或者用户多端下单。【相关推荐：Redis视频教程】

Maven 依赖

我主要是基于 Spring-Boot 2.1.2 + Jedis 进行实现

<?xmlversion="1.0"encoding="UTF-8"?><projectxmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.1.2.RELEASE</version></parent><groupId>cn.edu.cqvie</groupId><artifactId>redis-lock</artifactId><version>1.0-SNAPSHOT</version><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><java.version>1.8</java.version><redis.version>2.9.0</redis.version><spring-test.version>5.0.7</spring-test.version></properties><dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-autoconfigure</artifactId></dependency><dependency><groupId>org.springframework.data</groupId><artifactId>spring-data-redis</artifactId></dependency><dependency><groupId>redis.clients</groupId><artifactId>jedis</artifactId><version>${redis.version}</version></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-logging</artifactId></dependency><dependency><groupId>org.slf4j</groupId><artifactId>log4j-over-slf4j</artifactId></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency></dependencies><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></build></project>

配置文件

application.properties 配置文件内容如下：

spring.redis.host=127.0.0.1spring.redis.port=6379spring.redis.password=spring.redis.timeout=30000spring.redis.jedis.pool.max-active=8spring.redis.jedis.pool.min-idle=2spring.redis.jedis.pool.max-idle=4logging.level.root=INFO

接口定义

接口定义，对于锁我们核心其实就连个方法 lock 和 unlock.

publicinterfaceRedisLock{longTIMEOUT_MILLIS=30000;intRETRY_MILLIS=30000;longSLEEP_MILLIS=10;booleantryLock(Stringkey);booleanlock(Stringkey);booleanlock(Stringkey,longexpire);booleanlock(Stringkey,longexpire,longretryTimes);booleanunlock(Stringkey);}

分布式锁实现

我的实现方式是通过 setnx 方式实现了，如果存在 tryLock 逻辑的话，会通过 自旋 的方式重试

//AbstractRedisLock.java抽象类publicabstractclassAbstractRedisLockimplementsRedisLock{@Overridepublicbooleanlock(Stringkey){returnlock(key,TIMEOUT_MILLIS);}@Overridepublicbooleanlock(Stringkey,longexpire){returnlock(key,TIMEOUT_MILLIS,RETRY_MILLIS);}}//具体实现@ComponentpublicclassRedisLockImplextendsAbstractRedisLock{privateLoggerlogger=LoggerFactory.getLogger(getClass());@AutowiredprivateRedisTemplate<String,String>redisTemplate;privateThreadLocal<String>threadLocal=newThreadLocal<String>();privatestaticfinalStringUNLOCK_LUA;static{StringBuildersb=newStringBuilder();sb.append("ifredis.call(\"get\",KEYS[1])==ARGV[1]");sb.append("then");sb.append("returnredis.call(\"del\",KEYS[1])");sb.append("else");sb.append("return0");sb.append("end");UNLOCK_LUA=sb.toString();}@OverridepublicbooleantryLock(Stringkey){returntryLock(key,TIMEOUT_MILLIS);}publicbooleantryLock(Stringkey,longexpire){try{return!StringUtils.isEmpty(redisTemplate.execute((RedisCallback<String>)connection->{JedisCommandscommands=(JedisCommands)connection.getNativeConnection();Stringuuid=UUID.randomUUID().toString();threadLocal.set(uuid);returncommands.set(key,uuid,"NX","PX",expire);}));}catch(Throwablee){logger.error("setredisoccurredanexception",e);}returnfalse;}@Overridepublicbooleanlock(Stringkey,longexpire,longretryTimes){booleanresult=tryLock(key,expire);while(!result&&retryTimes-->0){try{logger.debug("lockfailed,retrying...{}",retryTimes);Thread.sleep(SLEEP_MILLIS);}catch(InterruptedExceptione){returnfalse;}result=tryLock(key,expire);}returnresult;}@Overridepublicbooleanunlock(Stringkey){try{List<String>keys=Collections.singletonList(key);List<String>args=Collections.singletonList(threadLocal.get());Longresult=redisTemplate.execute((RedisCallback<Long>)connection->{ObjectnativeConnection=connection.getNativeConnection();if(nativeConnectioninstanceofJedisCluster){return(Long)((JedisCluster)nativeConnection).eval(UNLOCK_LUA,keys,args);}if(nativeConnectioninstanceofJedis){return(Long)((Jedis)nativeConnection).eval(UNLOCK_LUA,keys,args);}return0L;});returnresult!=null&&result>0;}catch(Throwablee){logger.error("unlockoccurredanexception",e);}returnfalse;}}

测试代码

最后再来看看如何使用吧. (下面是一个模拟秒杀的场景)

@RunWith(SpringRunner.class)@SpringBootTestpublicclassRedisLockImplTest{privateLoggerlogger=LoggerFactory.getLogger(getClass());@AutowiredprivateRedisLockredisLock;@AutowiredprivateStringRedisTemplateredisTemplate;privateExecutorServiceexecutors=Executors.newScheduledThreadPool(8);@Testpublicvoidlock(){//初始化库存redisTemplate.opsForValue().set("goods-seckill","10");List<Future>futureList=newArrayList<>();for(inti=0;i<100;i++){futureList.add(executors.submit(this::seckill));try{Thread.sleep(100);}catch(InterruptedExceptione){e.printStackTrace();}}//等待结果，防止主线程退出futureList.forEach(action->{try{action.get();}catch(InterruptedException|ExecutionExceptione){e.printStackTrace();}});}publicintseckill(){Stringkey="goods";try{redisLock.lock(key);intnum=Integer.valueOf(Objects.requireNonNull(redisTemplate.opsForValue().get("goods-seckill")));if(num>0){redisTemplate.opsForValue().set("goods-seckill",String.valueOf(--num));logger.info("秒杀成功，剩余库存：{}",num);}else{logger.error("秒杀失败，剩余库存：{}",num);}returnnum;}catch(Throwablee){logger.error("seckillexception",e);}finally{redisLock.unlock(key);}return0;}}总结

本文是 Redis 锁的一种简单的实现方式，基于 jedis 实现了锁的重试操作。但是缺点还是有的，不支持锁的自动续期，锁的重入，以及公平性（目前通过自旋的方式实现，相当于是非公平的方式）。

“怎么理解Redis中的分布式锁”的内容就介绍到这里了，感谢大家的阅读。如果想了解更多行业相关的知识可以关注亿速云网站，小编将为大家输出更多高质量的实用文章！