导读#

大家都听过1万小时定律，可事实真的是这样吗？做了1万小时的CRUD，不还只会CRUD吗，这年头不适当的更新自身下技术栈，出门和别人聊天吹牛的时候

面试专题#

什么是分布式锁？#

首先，为了确保分布式锁可用，至少要满足以下三个条件

1. 互斥性。在任意时刻，只有一个客户端能持有锁
2. 不会发生死锁。即便有一个客户端在持有锁的期间奔溃而没有主动解锁，也能保证后续其他客户端能加锁
3. 解铃还须系铃人。加锁和解锁必须是同一个客户端，客户端自己不能把别人加的锁给解了

实现分布式锁方式？#

两种实现，下面都会有讲到

1. 采用lua脚本操作分布式锁
2. 采用setnx、setex命令连用的方式实现分布式锁

分布式锁的场景#

什么是分布式锁？#

• 分布式锁是控制分布式系统或不同系统之间共同访问共享资源的一种锁实现
• 如果不同的系统或同一个系统的不同主机之间共享了某个资源时，往往通过互斥来防止彼此干扰

为什么要有分布式锁？#

可以保证在分布式部署的应用集群中，同一个方法在同一操作只能被****一台机器上的一个线程执行。

设计要求#

1. 可重入锁(避免死锁)
2. 获取锁和释放锁高可用
3. 获取锁和释放锁高性能

实现方案#

1. 获取锁，使用setnx()：SETNX key val：当且仅当key不存在时，set一个key为val的字符串，返回1
2. 若key存在，则什么都不做，返回【0】加锁，锁的value值为当前占有锁服务器内网IP编号拼接任务标识
3. 在释放锁的时候进行判断。并使用expire命令为锁添加一个超时时间，超过该时间则自动释放锁
4. 返回1则成功获取锁。还设置一个获取的超时时间，若超过这个时间则放弃获取锁，setex(key,value,expire)过期以秒为单位
5. 释放锁的时候，判断是不是该锁(即value为当前服务器内网IP编号拼接任务标识)，若是该锁，则执行delete进行锁释放

Redis分布式锁的实现#

创建一个SpringBoot工程#

网址：https://start.spring.io/

image

步骤#

1、启动类上加上注解@EnableScheduling

2、执行方法上加上注解@Scheduled

image

打包并上传至Linux服务器中启动#

准备3台Linux服务器，并将打好的jar包，上传至3台服务器中，然后启动

image

nohub之持久化启动方式 #

nohup java -jar jar名称 &

查看集群里面所有集群是否启动成功

1、先安装lsof：yum install lsof 2、验证：lsof -i:8080

TCP三次握手#

查看本机TCP连接状态#

netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'

为什么要三次握手？#

主要是为了防止已失效的连接请求报文段突然又传到了B，因而报文错乱问题，假定A发出的第一个连接请求报文段并没有丢失，而是在某些网络节点长时间滞留，一直延迟到连接释放以后的某个时间才到达B，本来这是一个早已经失效的报文段。但B收到失效的连接请求报文段后，就误认为是A又发出一个新的连接请求，于是就向A发出确认报文段，同意建立连接。

假定不采用三次握手，那么只要B发出确认，新的连接就建立，这样一直等待A发来数据，B的许多资源就这样白白浪费了。

图解#

image

有3次握手了，为啥还有4次挥手？#

image

第一次挥手：主动关闭方发送一个FIN，用来关闭主动方到被动关闭方的数据传送，也就是主动关闭方告诉被动关闭方：我已经不 会再给你发数据了(当然，在fin包之前发送出去的数据，如果没有收到对应的ack确认报文，主动关闭方依然会重发这些数据)，但是，此时主动关闭方还可 以接受数据。
第二次挥手：被动关闭方收到FIN包后，发送一个ACK给对方，确认序号为收到序号+1（与SYN相同，一个FIN占用一个序号）。
第三次挥手：被动关闭方发送一个FIN，用来关闭被动关闭方到主动关闭方的数据传送，也就是告诉主动关闭方，我的数据也发送完了，不会再给你发数据了。
第四次挥手：主动关闭方收到FIN后，发送一个ACK给被动关闭方，确认序号为收到序号+1，至此，完成四次挥手。

作用#

确保数据能够完整传输

Redis分布式锁实现源码讲解#

图文讲解#

image

步骤#

1. 分布式锁满足两个条件，一个是加有效时间的锁，一个是高性能解锁
2. 采用redis命令setnx (set if not exist)、setex（set expire value）实现
3. 解锁流程不能遗漏，否则导致任务执行一次就永不过期
4. 将加锁代码和任务逻辑放到try catch代码块，解锁流程放到finally代码块

项目结构#

pom.xml#

<pre class="prettyprint prettyprinted" style="margin: 0px; padding: 0px; overflow-wrap: break-word; font-family: inherit !important; font-size: 12px !important; color: rgb(101, 108, 115);"><?xml version="1.0" encoding="UTF-8"?> <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://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>2.3.3.RELEASE</version> <relativePath/> </parent> <groupId>com.cyb</groupId> <artifactId>yb-mobile-redis</artifactId> <version>0.0.1-SNAPSHOT</version> <name>yb-mobile-redis</name> <description>Demo project for Spring Boot</description> <properties> <java.version>1.8</java.version> </properties> <dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-redis</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> <exclusions> <exclusion> <groupId>org.junit.vintage</groupId> <artifactId>junit-vintage-engine</artifactId> </exclusion> </exclusions> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project></pre>

application.properties#

<pre class="prettyprint prettyprinted" style="margin: 0px; padding: 0px; overflow-wrap: break-word; font-family: inherit !important; font-size: 12px !important; color: rgb(101, 108, 115);">spring.redis.database=0 spring.redis.host=192.168.199.142 spring.redis.port=6379 spring.redis.password=12345678 server.port=9001</pre>

RedisService.java#

<pre class="prettyprint prettyprinted" style="margin: 0px; padding: 0px; overflow-wrap: break-word; font-family: inherit !important; font-size: 12px !important; color: rgb(101, 108, 115);">package com.cyb.ybmobileredis.service; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.data.redis.core.; import org.springframework.stereotype.Service; import java.io.Serializable; import java.util.List; import java.util.Set; import java.util.concurrent.TimeUnit; /* * @ClassName：RedisService

• @Description：TODO
• @Author：chenyb
• @Date：2020/8/16 5:39 下午
• @Versiion：1.0 / @Service public class RedisService { @Autowired private RedisTemplate redisTemplate; private static double size = Math.pow(2, 32); /* * 写入缓存
  • @param key
  • @param offset 位 8Bit=1Byte
  • @return / public boolean setBit(String key, long offset, boolean isShow) { boolean result = false; try { ValueOperations<Serializable, Object> operations = redisTemplate.opsForValue(); operations.setBit(key, offset, isShow); result = true; } catch (Exception e) { e.printStackTrace(); } return result; } /* * 写入缓存
  • @param key
  • @param offset
  • @return / public boolean getBit(String key, long offset) { boolean result = false; try { ValueOperations<Serializable, Object> operations = redisTemplate.opsForValue(); result = operations.getBit(key, offset); } catch (Exception e) { e.printStackTrace(); } return result; } /* * 写入缓存
  • @param key
  • @param value
  • @return / public boolean set(final String key, Object value) { boolean result = false; try { ValueOperations<Serializable, Object> operations = redisTemplate.opsForValue(); operations.set(key, value); result = true; } catch (Exception e) { e.printStackTrace(); } return result; } /* * 写入缓存设置时效时间
  • @param key
  • @param value
  • @return / public boolean set(final String key, Object value, Long expireTime) { boolean result = false; try { ValueOperations<Serializable, Object> operations = redisTemplate.opsForValue(); operations.set(key, value); redisTemplate.expire(key, expireTime, TimeUnit.SECONDS); result = true; } catch (Exception e) { e.printStackTrace(); } return result; } /* * 批量删除对应的value
  • @param keys / public void remove(final String... keys) { for (String key : keys) { remove(key); } } /* * 删除对应的value
  • @param key / public void remove(final String key) { if (exists(key)) { redisTemplate.delete(key); } } /* * 判断缓存中是否有对应的value
  • @param key
  • @return / public boolean exists(final String key) { return redisTemplate.hasKey(key); } /* * 读取缓存
  • @param key
  • @return / public Object get(final String key) { Object result = null; ValueOperations<Serializable, Object> operations = redisTemplate.opsForValue(); result = operations.get(key); return result; } /* * 哈希 添加
  • @param key
  • @param hashKey
  • @param value / public void hmSet(String key, Object hashKey, Object value) { HashOperations<String, Object, Object> hash = redisTemplate.opsForHash(); hash.put(key, hashKey, value); } /* * 哈希获取数据
  • @param key
  • @param hashKey
  • @return / public Object hmGet(String key, Object hashKey) { HashOperations<String, Object, Object> hash = redisTemplate.opsForHash(); return hash.get(key, hashKey); } /* * 列表添加
  • @param k
  • @param v / public void lPush(String k, Object v) { ListOperations<String, Object> list = redisTemplate.opsForList(); list.rightPush(k, v); } /* * 列表获取
  • @param k
  • @param l
  • @param l1
  • @return / public List<Object> lRange(String k, long l, long l1) { ListOperations<String, Object> list = redisTemplate.opsForList(); return list.range(k, l, l1); } /* * 集合添加
  • @param key
  • @param value / public void add(String key, Object value) { SetOperations<String, Object> set = redisTemplate.opsForSet(); set.add(key, value); } /* * 集合获取
  • @param key
  • @return / public Set<Object> setMembers(String key) { SetOperations<String, Object> set = redisTemplate.opsForSet(); return set.members(key); } /* * 有序集合添加
  • @param key
  • @param value
  • @param scoure / public void zAdd(String key, Object value, double scoure) { ZSetOperations<String, Object> zset = redisTemplate.opsForZSet(); zset.add(key, value, scoure); } /* * 有序集合获取
  • @param key
  • @param scoure
  • @param scoure1
  • @return / public Set<Object> rangeByScore(String key, double scoure, double scoure1) { ZSetOperations<String, Object> zset = redisTemplate.opsForZSet(); redisTemplate.opsForValue(); return zset.rangeByScore(key, scoure, scoure1); } //第一次加载的时候将数据加载到redis中 public void saveDataToRedis(String name) { double index = Math.abs(name.hashCode() % size); long indexLong = new Double(index).longValue(); boolean availableUsers = setBit("availableUsers", indexLong, true); } //第一次加载的时候将数据加载到redis中 public boolean getDataToRedis(String name) { double index = Math.abs(name.hashCode() % size); long indexLong = new Double(index).longValue(); return getBit("availableUsers", indexLong); } /* * 有序集合获取排名
  • @param key 集合名称
  • @param value 值 / public Long zRank(String key, Object value) { ZSetOperations<String, Object> zset = redisTemplate.opsForZSet(); return zset.rank(key,value); } /* * 有序集合获取排名
  • @param key / public Set<ZSetOperations.TypedTuple<Object>> zRankWithScore(String key, long start,long end) { ZSetOperations<String, Object> zset = redisTemplate.opsForZSet(); Set<ZSetOperations.TypedTuple<Object>> ret = zset.rangeWithScores(key,start,end); return ret; } /* * 有序集合添加
  • @param key
  • @param value / public Double zSetScore(String key, Object value) { ZSetOperations<String, Object> zset = redisTemplate.opsForZSet(); return zset.score(key,value); } /* * 有序集合添加分数
  • @param key
  • @param value
  • @param scoure / public void incrementScore(String key, Object value, double scoure) { ZSetOperations<String, Object> zset = redisTemplate.opsForZSet(); zset.incrementScore(key, value, scoure); } /* * 有序集合获取排名
  • @param key / public Set<ZSetOperations.TypedTuple<Object>> reverseZRankWithScore(String key, long start,long end) { ZSetOperations<String, Object> zset = redisTemplate.opsForZSet(); Set<ZSetOperations.TypedTuple<Object>> ret = zset.reverseRangeByScoreWithScores(key,start,end); return ret; } /* * 有序集合获取排名
  • @param key */ public Set<ZSetOperations.TypedTuple<Object>> reverseZRankWithRank(String key, long start, long end) { ZSetOperations<String, Object> zset = redisTemplate.opsForZSet(); Set<ZSetOperations.TypedTuple<Object>> ret = zset.reverseRangeWithScores(key, start, end); return ret; } }</pre>

LockNxExJob.java#

<pre class="prettyprint prettyprinted" style="margin: 0px; padding: 0px; overflow-wrap: break-word; font-family: inherit !important; font-size: 12px !important; color: rgb(101, 108, 115);">package com.cyb.ybmobileredis.schedule; import com.cyb.ybmobileredis.service.RedisService; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.data.redis.core.RedisTemplate; import org.springframework.scheduling.annotation.Scheduled; import org.springframework.stereotype.Service; import java.net.Inet4Address; import java.net.InetAddress; import java.net.NetworkInterface; import java.util.Enumeration; /** * @ClassName：LockNxExJob

• @Description：分布式获取锁和释放锁
• @Author：chenyb
• @Date：2020/8/16 5:44 下午
• @Versiion：1.0 / @Service public class LockNxExJob { private static final Logger logger = LoggerFactory.getLogger(LockNxExJob.class); @Autowired private RedisService redisService; @Autowired private RedisTemplate redisTemplate; private static String LOCK_PREFIX = "prefix_"; @Scheduled(fixedRate = 8000) public void lockJob() { String lock = LOCK_PREFIX + "LockNxExJob"; boolean nxRet=false; try{ //redistemplate setnx操作 nxRet = redisTemplate.opsForValue().setIfAbsent(lock,getHostIp()); Object lockValue = redisService.get(lock); System.out.println(lockValue); //获取锁失败 if(!nxRet){ String value = (String)redisService.get(lock); //打印当前占用锁的服务器IP logger.info(System.currentTimeMillis()+" get lock fail,lock belong to:{}",value); return; }else{ redisTemplate.opsForValue().set(lock,getHostIp(),3600); //获取锁成功 logger.info(System.currentTimeMillis()+" start lock lockNxExJob success"); Thread.sleep(4000); } }catch (Exception e){ logger.error("lock error",e); }finally { if (nxRet){ System.out.println("释放锁成功"); redisService.remove(lock); } } } /* * 获取本机内网IP地址方法
  • @return */ private static String getHostIp(){ try{ Enumeration<NetworkInterface> allNetInterfaces = NetworkInterface.getNetworkInterfaces(); while (allNetInterfaces.hasMoreElements()){ NetworkInterface netInterface = (NetworkInterface) allNetInterfaces.nextElement(); Enumeration<InetAddress> addresses = netInterface.getInetAddresses(); while (addresses.hasMoreElements()){ InetAddress ip = (InetAddress) addresses.nextElement(); if (ip != null && ip instanceof Inet4Address && !ip.isLoopbackAddress() //loopback地址即本机地址，IPv4的loopback范围是127.0.0.0 ~ 127.255.255.255 && ip.getHostAddress().indexOf(":")==-1){ return ip.getHostAddress(); } } } }catch(Exception e){ e.printStackTrace(); } return null; } }</pre>

验证#

打个jar运行在Linux上，一个在本地运行，一个获取锁成功，一个获取锁失败

image

Redis分布式锁可能出现的问题#

image

上面我们已经使用代码实现了分布式锁的功能，同一时刻****只能一把锁获取成功。从上图可以看出，极端情况下，第一个Server获取锁成功后，服务或者Redis宕机了，会导致Redis锁无法释放的问题，其他的Server就一直获取锁失败。

模拟server获取锁宕机#

先把项目跑起来，获取锁之后，立马kill -9 进程id，杀掉当前进程，然后在运行项目，控制台就会一直提示，获取锁失败了。

image

image

image

解决方案(重点)#

1. 一次性执行一条命令就不会出现该情况发生，采用Lua脚本
2. Redis从2.6之后，支持setnx、setex连用

lua脚本#

1. 在redource目录下新增一个后缀名为.lua结尾的文件
2. 编写lua脚本
3. 传入lua脚本的key和arg
4. 调用redisTemplate.execute方法执行脚本

编写lua脚本

image

<pre class="prettyprint prettyprinted" style="margin: 0px; padding: 0px; overflow-wrap: break-word; font-family: inherit !important; font-size: 12px !important; color: rgb(101, 108, 115);">local lockKey = KEYS[1] local lockValue = KEYS[2] -- setnx info local result_1 = redis.call('SETNX',lockKey,lockValue) if result_1 == true then local result_2 = redis.call('SETEX',lockKey,3600,lockValue) return result_1 else return result_1 end</pre>

封装调用lua脚本方法

image

<pre class="prettyprint prettyprinted" style="margin: 0px; padding: 0px; overflow-wrap: break-word; font-family: inherit !important; font-size: 12px !important; color: rgb(101, 108, 115);"> @Autowired private RedisTemplate redisTemplate; private DefaultRedisScript<Boolean> lockScript; /** * 获取lua结果
*
* @param key 键
* @param value 值
* @return */ public Boolean luaExpress(String key, String value) { lockScript = new DefaultRedisScript<>(); lockScript.setScriptSource( new ResourceScriptSource(new ClassPathResource("add.lua")) ); //设置返回值 lockScript.setResultType(Boolean.class); //封装参数 List<Object> keyList = new ArrayList<>(); keyList.add(key); keyList.add(value); Boolean result = (Boolean) redisTemplate.execute(lockScript, keyList); return result; }</pre>

改造之前的分布式锁方法

image

<pre class="prettyprint prettyprinted" style="margin: 0px; padding: 0px; overflow-wrap: break-word; font-family: inherit !important; font-size: 12px !important; color: rgb(101, 108, 115);">package com.cyb.ybmobileredis.schedule; import com.cyb.ybmobileredis.service.RedisService; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.core.io.ClassPathResource; import org.springframework.data.redis.core.RedisTemplate; import org.springframework.data.redis.core.script.DefaultRedisScript; import org.springframework.scheduling.annotation.Scheduled; import org.springframework.scripting.support.ResourceScriptSource; import org.springframework.stereotype.Service; import java.net.Inet4Address; import java.net.InetAddress; import java.net.NetworkInterface; import java.util.ArrayList; import java.util.Enumeration; import java.util.List; /** * @ClassName：LockNxExJob

• @Description：分布式获取锁和释放锁
• @Author：chenyb
• @Date：2020/8/16 5:44 下午
• @Versiion：1.0 / @Service public class LockNxExJob { private static final Logger logger = LoggerFactory.getLogger(LockNxExJob.class); @Autowired private RedisService redisService; @Autowired private RedisTemplate redisTemplate; private static String LOCK_PREFIX = "prefix_"; private DefaultRedisScript<Boolean> lockScript; //一般分布式锁 // @Scheduled(fixedRate = 8000) // public void lockJob() { // String lock = LOCK_PREFIX + "LockNxExJob"; // boolean nxRet = false; // try { // //redistemplate setnx操作 // nxRet = redisTemplate.opsForValue().setIfAbsent(lock, getHostIp()); // Object lockValue = redisService.get(lock); // System.out.println(lockValue); // //获取锁失败 // if (!nxRet) { // String value = (String) redisService.get(lock); // //打印当前占用锁的服务器IP // logger.info(System.currentTimeMillis() + " get lock fail,lock belong to:{}", value); // return; // } else { // redisTemplate.opsForValue().set(lock, getHostIp(), 3600000); // // //获取锁成功 // logger.info(System.currentTimeMillis() + " start lock lockNxExJob success"); // Thread.sleep(4000); // } // } catch (Exception e) { // logger.error("lock error", e); // // } finally { // if (nxRet) { // System.out.println("释放锁成功"); // redisService.remove(lock); // } // } // } /* * lua脚本方式分布式锁 / @Scheduled(fixedRate = 8000) public void luaLockJob() { String lock = LOCK_PREFIX + "LockNxExJob"; boolean nxRet = false; try { //redistemplate setnx操作 nxRet = luaExpress(lock,getHostIp()); Object lockValue = redisService.get(lock); System.out.println(lockValue); //获取锁失败 if (!nxRet) { String value = (String) redisService.get(lock); //打印当前占用锁的服务器IP logger.info(System.currentTimeMillis() + " lua get lock fail,lock belong to:{}", value); return; } else { redisTemplate.opsForValue().set(lock, getHostIp(), 3600000); //获取锁成功 logger.info(System.currentTimeMillis() + " lua start lock lockNxExJob success"); Thread.sleep(4000); } } catch (Exception e) { logger.error("lua lock error", e); } finally { if (nxRet) { System.out.println("lua 释放锁成功"); redisService.remove(lock); } } } /* * 获取lua结果
  • @param key 键
  • @param value 值
  • @return / public Boolean luaExpress(String key, String value) { lockScript = new DefaultRedisScript<>(); lockScript.setScriptSource( new ResourceScriptSource(new ClassPathResource("add.lua")) ); //设置返回值 lockScript.setResultType(Boolean.class); //封装参数 List<Object> keyList = new ArrayList<>(); keyList.add(key); keyList.add(value); Boolean result = (Boolean) redisTemplate.execute(lockScript, keyList); return result; } /* * 获取本机内网IP地址方法
  • @return */ private static String getHostIp() { try { Enumeration<NetworkInterface> allNetInterfaces = NetworkInterface.getNetworkInterfaces(); while (allNetInterfaces.hasMoreElements()) { NetworkInterface netInterface = (NetworkInterface) allNetInterfaces.nextElement(); Enumeration<InetAddress> addresses = netInterface.getInetAddresses(); while (addresses.hasMoreElements()) { InetAddress ip = (InetAddress) addresses.nextElement(); if (ip != null && ip instanceof Inet4Address && !ip.isLoopbackAddress() //loopback地址即本机地址，IPv4的loopback范围是127.0.0.0 ~ 127.255.255.255 && ip.getHostAddress().indexOf(":") == -1) { return ip.getHostAddress(); } } } } catch (Exception e) { e.printStackTrace(); } return null; } }</pre>

验证#

image

补充解决Redis中的key乱码问题#

只需要添加RedisConfig.java配置文件即可

image

<pre class="prettyprint prettyprinted" style="margin: 0px; padding: 0px; overflow-wrap: break-word; font-family: inherit !important; font-size: 12px !important; color: rgb(101, 108, 115);">package com.cyb.ybmobileredis.config; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.data.redis.connection.RedisConnectionFactory; import org.springframework.data.redis.core.RedisTemplate; import org.springframework.data.redis.serializer.RedisSerializer; import org.springframework.data.redis.serializer.StringRedisSerializer; /** * @ClassName：RedisConfig

• @Description：Redis配置类
• @Author：chenyb
• @Date：2020/8/16 11:48 下午
• @Versiion：1.0 */ @Configuration //当前类为配置类 public class RedisConfig { @Bean //redisTemplate注入到Spring容器 public RedisTemplate<String,String> redisTemplate(RedisConnectionFactory factory){ RedisTemplate<String,String> redisTemplate=new RedisTemplate<>(); RedisSerializer<String> redisSerializer = new StringRedisSerializer(); redisTemplate.setConnectionFactory(factory); //key序列化 redisTemplate.setKeySerializer(redisSerializer); //value序列化 redisTemplate.setValueSerializer(redisSerializer); //value hashmap序列化 redisTemplate.setHashKeySerializer(redisSerializer); //key hashmap序列化 redisTemplate.setHashValueSerializer(redisSerializer); return redisTemplate; } }</pre>

RedisConnection实现分布式锁#

简介

RedisConnection实现分布式锁的方式，采用redisTemplate操作redisConnection实现setnx和setex两个命令连用

代码实现

image

<pre class="prettyprint prettyprinted" style="margin: 0px; padding: 0px; overflow-wrap: break-word; font-family: inherit !important; font-size: 12px !important; color: rgb(101, 108, 115);">package com.cyb.ybmobileredis.schedule; import com.cyb.ybmobileredis.service.RedisService; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.core.io.ClassPathResource; import org.springframework.dao.DataAccessException; import org.springframework.data.redis.connection.RedisConnection; import org.springframework.data.redis.connection.RedisStringCommands; import org.springframework.data.redis.core.RedisCallback; import org.springframework.data.redis.core.RedisTemplate; import org.springframework.data.redis.core.script.DefaultRedisScript; import org.springframework.data.redis.core.types.Expiration; import org.springframework.scheduling.annotation.Scheduled; import org.springframework.scripting.support.ResourceScriptSource; import org.springframework.stereotype.Service; import java.net.Inet4Address; import java.net.InetAddress; import java.net.NetworkInterface; import java.util.ArrayList; import java.util.Enumeration; import java.util.List; /** * @ClassName：LockNxExJob

• @Description：分布式获取锁和释放锁
• @Author：chenyb
• @Date：2020/8/16 5:44 下午
• @Versiion：1.0 / @Service public class LockNxExJob { private static final Logger logger = LoggerFactory.getLogger(LockNxExJob.class); @Autowired private RedisService redisService; @Autowired private RedisTemplate redisTemplate; private static String LOCK_PREFIX = "prefix_"; private DefaultRedisScript<Boolean> lockScript; //一般分布式锁 // @Scheduled(fixedRate = 8000) // public void lockJob() { // String lock = LOCK_PREFIX + "LockNxExJob"; // boolean nxRet = false; // try { // //redistemplate setnx操作 // nxRet = redisTemplate.opsForValue().setIfAbsent(lock, getHostIp()); // Object lockValue = redisService.get(lock); // System.out.println(lockValue); // //获取锁失败 // if (!nxRet) { // String value = (String) redisService.get(lock); // //打印当前占用锁的服务器IP // logger.info(System.currentTimeMillis() + " get lock fail,lock belong to:{}", value); // return; // } else { // redisTemplate.opsForValue().set(lock, getHostIp(), 3600000); // // //获取锁成功 // logger.info(System.currentTimeMillis() + " start lock lockNxExJob success"); // Thread.sleep(4000); // } // } catch (Exception e) { // logger.error("lock error", e); // // } finally { // if (nxRet) { // System.out.println("释放锁成功"); // redisService.remove(lock); // } // } // } /* * lua脚本方式分布式锁 / // @Scheduled(fixedRate = 8000) // public void luaLockJob() { // String lock = LOCK_PREFIX + "LockNxExJob"; // boolean nxRet = false; // try { // //redistemplate setnx操作 // //nxRet = luaExpress(lock,getHostIp()); // nxRet = setLock(lock,600); // Object lockValue = redisService.get(lock); // System.out.println(lockValue); // //获取锁失败 // if (!nxRet) { // String value = (String) redisService.get(lock); // //打印当前占用锁的服务器IP // logger.info(System.currentTimeMillis() + " lua get lock fail,lock belong to:{}", value); // return; // } else { // redisTemplate.opsForValue().set(lock, getHostIp(), 3600000); // // //获取锁成功 // logger.info(System.currentTimeMillis() + " lua start lock lockNxExJob success"); // Thread.sleep(4000); // } // } catch (Exception e) { // logger.error("lua lock error", e); // // } finally { // if (nxRet) { // System.out.println("lua 释放锁成功"); // redisService.remove(lock); // } // } // } /* * setnx和setex连用分布式锁 / @Scheduled(fixedRate = 8000) public void setLockJob() { String lock = LOCK_PREFIX + "LockNxExJob"; boolean nxRet = false; try { //redistemplate setnx操作 //nxRet = luaExpress(lock,getHostIp()); nxRet = setLock(lock,getHostIp(),3); Object lockValue = redisService.get(lock); System.out.println(lockValue); //获取锁失败 if (!nxRet) { String value = (String) redisService.get(lock); //打印当前占用锁的服务器IP logger.info(System.currentTimeMillis() + " setnx and setex get lock fail,lock belong to:{}", value); return; } else { redisTemplate.opsForValue().set(lock, getHostIp(), 3600000); //获取锁成功 logger.info(System.currentTimeMillis() + " setnx and setex start lock lockNxExJob success"); Thread.sleep(4000); } } catch (Exception e) { logger.error(" setnx and setex lock error", e); } finally { if (nxRet) { System.out.println(" setnx and setex 释放锁成功"); redisService.remove(lock); } } } /* * setnx和setex连用
  • @param key 键
  • @param value 值
  • @param expire 超时时间
  • @return / public boolean setLock(String key,String value,long expire){ try{ Boolean result=(boolean)redisTemplate.execute(new RedisCallback<Boolean>() { @Override public Boolean doInRedis(RedisConnection connection) throws DataAccessException { return connection.set(key.getBytes(),value.getBytes(),Expiration.seconds(expire),RedisStringCommands.SetOption.ifAbsent()); } }); return result; }catch (Exception e){ logger.error("set redis occured an exception",e); } return false; } /* * 获取lua结果
  • @param key 键
  • @param value 值
  • @return / public Boolean luaExpress(String key, String value) { lockScript = new DefaultRedisScript<>(); lockScript.setScriptSource( new ResourceScriptSource(new ClassPathResource("add.lua")) ); //设置返回值 lockScript.setResultType(Boolean.class); //封装参数 List<Object> keyList = new ArrayList<>(); keyList.add(key); keyList.add(value); Boolean result = (Boolean) redisTemplate.execute(lockScript, keyList); return result; } /* * 获取本机内网IP地址方法
  • @return */ private static String getHostIp() { try { Enumeration<NetworkInterface> allNetInterfaces = NetworkInterface.getNetworkInterfaces(); while (allNetInterfaces.hasMoreElements()) { NetworkInterface netInterface = (NetworkInterface) allNetInterfaces.nextElement(); Enumeration<InetAddress> addresses = netInterface.getInetAddresses(); while (addresses.hasMoreElements()) { InetAddress ip = (InetAddress) addresses.nextElement(); if (ip != null && ip instanceof Inet4Address && !ip.isLoopbackAddress() //loopback地址即本机地址，IPv4的loopback范围是127.0.0.0 ~ 127.255.255.255 && ip.getHostAddress().indexOf(":") == -1) { return ip.getHostAddress(); } } } } catch (Exception e) { e.printStackTrace(); } return null; } }</pre>

测试#

image

分布式锁优化细节(重点)#

上面几个案例，已经实现了分布式锁的功能，但是极端情况下，ServerA程序还没执行完，ServerB程序执行完，把锁释放掉了，就会造成A的锁释放掉了，这不是扯嘛，ServerA还没执行完，锁就被其他人释放了。解决方案：释放的时候，使用lua，通过get方法获取value，判断value是否等于本机ip，是自己的才能释放

image

<pre class="prettyprint prettyprinted" style="margin: 0px; padding: 0px; overflow-wrap: break-word; font-family: inherit !important; font-size: 12px !important; color: rgb(101, 108, 115);">package com.cyb.ybmobileredis.schedule; import com.cyb.ybmobileredis.service.RedisService; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.core.io.ClassPathResource; import org.springframework.dao.DataAccessException; import org.springframework.data.redis.connection.RedisConnection; import org.springframework.data.redis.connection.RedisStringCommands; import org.springframework.data.redis.core.RedisCallback; import org.springframework.data.redis.core.RedisTemplate; import org.springframework.data.redis.core.script.DefaultRedisScript; import org.springframework.data.redis.core.types.Expiration; import org.springframework.scheduling.annotation.Scheduled; import org.springframework.scripting.support.ResourceScriptSource; import org.springframework.stereotype.Service; import java.net.Inet4Address; import java.net.InetAddress; import java.net.NetworkInterface; import java.util.ArrayList; import java.util.Enumeration; import java.util.List; /** * @ClassName：LockNxExJob

• @Description：分布式获取锁和释放锁
• @Author：chenyb
• @Date：2020/8/16 5:44 下午
• @Versiion：1.0 / @Service public class LockNxExJob { private static final Logger logger = LoggerFactory.getLogger(LockNxExJob.class); @Autowired private RedisService redisService; @Autowired private RedisTemplate redisTemplate; private static String LOCK_PREFIX = "prefix_"; private DefaultRedisScript<Boolean> lockScript; //一般分布式锁 // @Scheduled(fixedRate = 8000) // public void lockJob() { // String lock = LOCK_PREFIX + "LockNxExJob"; // boolean nxRet = false; // try { // //redistemplate setnx操作 // nxRet = redisTemplate.opsForValue().setIfAbsent(lock, getHostIp()); // Object lockValue = redisService.get(lock); // System.out.println(lockValue); // //获取锁失败 // if (!nxRet) { // String value = (String) redisService.get(lock); // //打印当前占用锁的服务器IP // logger.info(System.currentTimeMillis() + " get lock fail,lock belong to:{}", value); // return; // } else { // redisTemplate.opsForValue().set(lock, getHostIp(), 3600000); // // //获取锁成功 // logger.info(System.currentTimeMillis() + " start lock lockNxExJob success"); // Thread.sleep(4000); // } // } catch (Exception e) { // logger.error("lock error", e); // // } finally { // if (nxRet) { // System.out.println("释放锁成功"); // redisService.remove(lock); // } // } // } /* * lua脚本方式分布式锁 / // @Scheduled(fixedRate = 8000) // public void luaLockJob() { // String lock = LOCK_PREFIX + "LockNxExJob"; // boolean nxRet = false; // try { // //redistemplate setnx操作 // //nxRet = luaExpress(lock,getHostIp()); // nxRet = setLock(lock,600); // Object lockValue = redisService.get(lock); // System.out.println(lockValue); // //获取锁失败 // if (!nxRet) { // String value = (String) redisService.get(lock); // //打印当前占用锁的服务器IP // logger.info(System.currentTimeMillis() + " lua get lock fail,lock belong to:{}", value); // return; // } else { // redisTemplate.opsForValue().set(lock, getHostIp(), 3600000); // // //获取锁成功 // logger.info(System.currentTimeMillis() + " lua start lock lockNxExJob success"); // Thread.sleep(4000); // } // } catch (Exception e) { // logger.error("lua lock error", e); // // } finally { // if (nxRet) { // System.out.println("lua 释放锁成功"); // redisService.remove(lock); // } // } // } /* * setnx和setex连用分布式锁 / @Scheduled(fixedRate = 8000) public void setLockJob() { String lock = LOCK_PREFIX + "LockNxExJob"; boolean nxRet = false; try { //redistemplate setnx操作 //nxRet = luaExpress(lock,getHostIp()); System.out.println("hostIp1="+getHostIp()); nxRet = setLock(lock, getHostIp(), 30); Object lockValue = redisService.get(lock); System.out.println(lockValue); //获取锁失败 if (!nxRet) { String value = (String) redisService.get(lock); //打印当前占用锁的服务器IP logger.info(System.currentTimeMillis() + " setnx and setex get lock fail,lock belong to:{}", value); return; } else { //获取锁成功 logger.info(System.currentTimeMillis() + " setnx and setex start lock lockNxExJob success"); Thread.sleep(4000); } } catch (Exception e) { logger.error(" setnx and setex lock error", e); } finally { if (nxRet) { System.out.println(" setnx and setex 释放锁成功"); //redisService.remove(lock); //使用lua脚本释放锁 System.out.println("hostIp2="+getHostIp()); Boolean result = releaseLock(lock, getHostIp()); System.out.println("状态:"+result); } } } /* * 释放锁操作
  • @param key 键
  • @param value 值
  • @return / private boolean releaseLock(String key, String value) { lockScript = new DefaultRedisScript<Boolean>(); lockScript.setScriptSource(new ResourceScriptSource(new ClassPathResource("unlock.lua"))); lockScript.setResultType(Boolean.class); //封装参数 List<Object> keyList = new ArrayList<>(); keyList.add(key); keyList.add(value); Boolean result = (Boolean) redisTemplate.execute(lockScript, keyList); return result; } /* * setnx和setex连用
  • @param key 键
  • @param value 值
  • @param expire 超时时间
  • @return / public boolean setLock(String key, String value, long expire) { try { Boolean result = (boolean) redisTemplate.execute(new RedisCallback<Boolean>() { @Override public Boolean doInRedis(RedisConnection connection) throws DataAccessException { return connection.set(key.getBytes(), value.getBytes(), Expiration.seconds(expire), RedisStringCommands.SetOption.ifAbsent()); } }); return result; } catch (Exception e) { logger.error("set redis occured an exception", e); } return false; } /* * 获取lua结果
  • @param key 键
  • @param value 值
  • @return / public Boolean luaExpress(String key, String value) { lockScript = new DefaultRedisScript<>(); lockScript.setScriptSource( new ResourceScriptSource(new ClassPathResource("add.lua")) ); //设置返回值 lockScript.setResultType(Boolean.class); //封装参数 List<Object> keyList = new ArrayList<>(); keyList.add(key); keyList.add(value); Boolean result = (Boolean) redisTemplate.execute(lockScript, keyList); return result; } /* * 获取本机内网IP地址方法
  • @return */ private static String getHostIp() { try { Enumeration<NetworkInterface> allNetInterfaces = NetworkInterface.getNetworkInterfaces(); while (allNetInterfaces.hasMoreElements()) { NetworkInterface netInterface = (NetworkInterface) allNetInterfaces.nextElement(); Enumeration<InetAddress> addresses = netInterface.getInetAddresses(); while (addresses.hasMoreElements()) { InetAddress ip = (InetAddress) addresses.nextElement(); if (ip != null && ip instanceof Inet4Address && !ip.isLoopbackAddress() //loopback地址即本机地址，IPv4的loopback范围是127.0.0.0 ~ 127.255.255.255 && ip.getHostAddress().indexOf(":") == -1) { return ip.getHostAddress(); } } } } catch (Exception e) { e.printStackTrace(); } return null; } }</pre>

unlock.lua脚本#

image

<pre class="prettyprint prettyprinted" style="margin: 0px; padding: 0px; overflow-wrap: break-word; font-family: inherit !important; font-size: 12px !important; color: rgb(101, 108, 115);">local lockKey = KEYS[1] local lockValue = KEYS[2] -- get key local result_1 = redis.call('get', lockKey) if result_1 == lockValue then local result_2= redis.call('del', lockKey) return result_2 else return false end</pre>

演示#

为了演示方便，我把失效时间设置短一点，8秒

image

尾声#

嫖都嫖完了，难道你忍心不点赞关注嘛，O(∩_∩)O哈哈~~~~~今天，先到这，后续继续写Redis秒杀系统的设计。