面试题:
- Redis除了拿来做缓存,你还见过基于Redis的什么用法?
1.数据共享,分布式Session
2.分布式锁
3.全局ID
4.计算器、点赞
5.位统计
6.购物车
7.轻量级消息队列:list、stream
8.抽奖
9.点赞、签到、打卡
10.差集交集并集,用户关注、可能认识的人,推荐模型
11.热点新间、热搜排行榜
- Redis做分布式锁的时候有需要注意的问题?
- 你们公司自己实现的分布式锁是否用的setnx命令实现?这个是最合适的吗?你如何考虑分布式锁的可重入问题?
- 如果是Redis是单点部署的,会带来什么问题?那你准备怎么解决单点问题呢?
- Redis集群模式下,比如主从模式,CAP方面有没有什么问题呢?
- 那你简单的介绍一下Redlock吧?你简历上写redisson,你谈谈
- Redis分布式锁如何续期?看门狗知道吗?
分布式锁需要具备的条件和刚需
独占性
OnlyOne,任何时刻只能有且仅有一个线程持有
高可用
若redis集群环境下,不能因为某一个节点挂了而出现获取锁和释放锁失败的情况;高并发请求下,依旧性能OK好使
防死锁
杜绝死锁,必须有超时控制机制或者撤销操作,有个兜底终止跳出方案
不乱抢
防止张冠李戴,不能私下unlock别人的锁,只能自己加锁自己释放,自己约的锁含着泪也要自己解
重入性
同一个节点的同一个线程如果获得锁之后,它也可以再次获取这个锁
分布式锁
官网:set 命令
使用set进行占锁,删掉key代表锁释放。
setnx key value
注:setnx+expire不安全,两条命令非原子性的。
set key value [EX seconds] [PX milliseconds] [NX|XX]
重点:JUC中AQS锁的规范落地参考+可重入锁考虑+Lua脚本+Redist命令一步步实现分布式锁
案例
V1.0 版本(基础案例)
使用场景:多个服务间保证同一时刻同一时间段内同一用户只能有一个请求(防止关键业务出现并发攻击)。
1、pom.xml文件
<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.atguigu.redislock</groupId><artifactId>redis_distributed_lock2</artifactId><version>1.0-SNAPSHOT</version><parent><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-parent</artifactId><version>2.6.12</version><relativePath/> <!-- lookup parent from repository --></parent><properties><project.build.sourceEncoding>UTF-8</project.build.sourceEncoding><maven.compiler.source>8</maven.compiler.source><maven.compiler.target>8</maven.compiler.target><lombok.version>1.16.18</lombok.version></properties><dependencies><!--SpringBoot通用依赖模块--><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><!--SpringBoot与Redis整合依赖--><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-data-redis</artifactId></dependency><dependency><groupId>org.apache.commons</groupId><artifactId>commons-pool2</artifactId></dependency><!--swagger2--><dependency><groupId>io.springfox</groupId><artifactId>springfox-swagger2</artifactId><version>2.9.2</version></dependency><dependency><groupId>io.springfox</groupId><artifactId>springfox-swagger-ui</artifactId><version>2.9.2</version></dependency><!--通用基础配置boottest/lombok/hutool--><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>${lombok.version}</version><optional>true</optional></dependency><dependency><groupId>cn.hutool</groupId><artifactId>hutool-all</artifactId><version>5.8.8</version></dependency></dependencies><build><plugins><plugin><groupId>org.springframework.boot</groupId><artifactId>spring-boot-maven-plugin</artifactId></plugin></plugins></build></project>
2、ymal文件
server.port=7777spring.application.name=redis_distributed_lock
# ========================swagger2=====================
# http://localhost:7777/swagger-ui.html
swagger2.enabled=true
spring.mvc.pathmatch.matching-strategy=ant_path_matcher# ========================redis单机=====================
spring.redis.database=0
spring.redis.host=192.168.111.185
spring.redis.port=6379
spring.redis.password=111111
spring.redis.lettuce.pool.max-active=8
spring.redis.lettuce.pool.max-wait=-1ms
spring.redis.lettuce.pool.max-idle=8
spring.redis.lettuce.pool.min-idle=0
3、主启动类
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;@SpringBootApplication
public class RedisDistributedLockApp {public static void main(String[] args) {SpringApplication.run(RedisDistributedLockApp.class,args);}
}
4、配置类
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.mvc.method.RequestMappingInfoHandlerMapping;
import springfox.documentation.builders.ApiInfoBuilder;
import springfox.documentation.builders.PathSelectors;
import springfox.documentation.builders.RequestHandlerSelectors;
import springfox.documentation.service.ApiInfo;
import springfox.documentation.spi.DocumentationType;
import springfox.documentation.spring.web.plugins.Docket;
import springfox.documentation.spring.web.plugins.WebMvcRequestHandlerProvider;
import springfox.documentation.swagger2.annotations.EnableSwagger2;import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.List;
import java.util.stream.Collectors;@Configuration
@EnableSwagger2
public class Swagger2Config {@Value("${swagger2.enabled}")private Boolean enabled;@Beanpublic Docket createRestApi() {return new Docket(DocumentationType.SWAGGER_2).apiInfo(apiInfo()).enable(enabled).select().apis(RequestHandlerSelectors.basePackage("com.atguigu.redislock")) //你自己的package.paths(PathSelectors.any()).build();}private ApiInfo apiInfo() {return new ApiInfoBuilder().title("springboot利用swagger2构建api接口文档 "+"\t"+ DateTimeFormatter.ofPattern("yyyy-MM-dd").format(LocalDateTime.now())).description("springboot+redis整合").version("1.0").termsOfServiceUrl("https://www.baidu.com/").build();}}
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.data.redis.connection.lettuce.LettuceConnectionFactory;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.serializer.GenericJackson2JsonRedisSerializer;
import org.springframework.data.redis.serializer.StringRedisSerializer;@Configuration
public class RedisConfig {@Beanpublic RedisTemplate<String, Object> redisTemplate(LettuceConnectionFactory lettuceConnectionFactory) {RedisTemplate<String,Object> redisTemplate = new RedisTemplate<>();redisTemplate.setConnectionFactory(lettuceConnectionFactory);//设置key序列化方式stringredisTemplate.setKeySerializer(new StringRedisSerializer());//设置value的序列化方式jsonredisTemplate.setValueSerializer(new GenericJackson2JsonRedisSerializer());redisTemplate.setHashKeySerializer(new StringRedisSerializer());redisTemplate.setHashValueSerializer(new GenericJackson2JsonRedisSerializer());redisTemplate.afterPropertiesSet();return redisTemplate;}
}
5、业务类
import cn.hutool.core.util.IdUtil;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;@Service
@Slf4j
public class InventoryService {@Autowiredprivate StringRedisTemplate stringRedisTemplate;@Value("${server.port}")private String port;public String sale() {String retMessage = "";try {//1 查询库存信息String result = stringRedisTemplate.opsForValue().get("inventory001");//2 判断库存是否足够Integer inventoryNumber = result == null ? 0 : Integer.parseInt(result);//3 扣减库存if(inventoryNumber > 0) {stringRedisTemplate.opsForValue().set("inventory001",String.valueOf(--inventoryNumber));retMessage = "成功卖出一个商品,库存剩余: "+inventoryNumber;System.out.println(retMessage);}else{retMessage = "商品卖完了,o(╥﹏╥)o";}} finally {// 释放操作}return retMessage+"\t"+"服务端口号:"+port;}
}
import cn.hutool.core.util.IdUtil;
import com.atguigu.redislock.service.InventoryService;
import io.swagger.annotations.Api;
import io.swagger.annotations.ApiOperation;
import lombok.Getter;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.ResponseStatus;
import org.springframework.web.bind.annotation.RestController;import java.util.concurrent.atomic.AtomicInteger;@RestController
@Api(tags = "redis分布式锁测试")
public class InventoryController {@Autowiredprivate InventoryService inventoryService;@ApiOperation("扣减库存,一次卖一个")@GetMapping(value = "/inventory/sale")public String sale() {return inventoryService.sale();}
}
丝袜哥测试地址:http://localhost:7777/swagger-ui.html#/
V2.0 版本
使用 synchronized 或者 lock 进行加锁操作
import cn.hutool.core.util.IdUtil;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;@Service
@Slf4j
public class InventoryService {@Autowiredprivate StringRedisTemplate stringRedisTemplate;@Value("${server.port}")private String port;private Lock lock = new ReentrantLock();public String sale() {String retMessage = "";lock.lock();try {//1 查询库存信息String result = stringRedisTemplate.opsForValue().get("inventory001");//2 判断库存是否足够Integer inventoryNumber = result == null ? 0 : Integer.parseInt(result);//3 扣减库存if(inventoryNumber > 0) {stringRedisTemplate.opsForValue().set("inventory001",String.valueOf(--inventoryNumber));retMessage = "成功卖出一个商品,库存剩余: "+inventoryNumber;System.out.println(retMessage);}else{retMessage = "商品卖完了,o(╥﹏╥)o";}}finally {lock.unlock();}return retMessage+"\t"+"服务端口号:"+port;}
}
若在添加一个相同服务,另一个服务为8888端口,使用 nginx 轮训访问 7777 和 8888 服务,此时就会出现超卖现象。lock 只针对当前服务有用,锁不了其他服务。
Nginx配置负载均衡
1、常用命令
检查nginx.conf文件合法性:
nginx -t -c ./conf/nginx.conf
检查nginx服务是否启动:
tasklist /fi "imagename eq nginx.exe"
启动nginx:
start nginx 或 ./nginx
重新加载:
nginx -s reload
停止服务:
nginx -s stop
2、配置文件
服务测试
启动 7777 和 8888 服务,通过Nginx访问,你的Linux服务器地址lP,反向代理+负裁均衡,可以点击看到效果,一边一个,默认轮询:http://192.168.0.185/inventory/sale
使用 jmeter 进行压测
http请求:
测试结果:
异常:76号商品被卖出2次,出现超卖故章现象。
结论
在单机环境下,可以使用synchronized或Lock来实现。
但是在分布式系统中,因为竞争的线程可能不在同一个节点上(同一个jvm中),所以需要一个让所有进程都能访问到的锁来实现(比如redis或者zookeeper来构建)。
不同进程jvm层面的锁就不管用了,那么可以利用第三方的一个组件,来获取锁,未获取到锁,则阻塞当前想要运行的线程。
V3.1 版本
使用递归进行重试
import cn.hutool.core.util.IdUtil;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;@Service
@Slf4j
public class InventoryService {@Autowiredprivate StringRedisTemplate stringRedisTemplate;@Value("${server.port}")private String port;private Lock lock = new ReentrantLock();public String sale() {String retMessage = "";String key = "zzyyRedisLock";String uuidValue = IdUtil.simpleUUID()+":"+Thread.currentThread().getId();Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(key, uuidValue);if(!flag){//暂停20毫秒后递归调用try { TimeUnit.MILLISECONDS.sleep(20); } catch (InterruptedException e) { e.printStackTrace(); }sale();}else{try{//1 查询库存信息String result = stringRedisTemplate.opsForValue().get("inventory001");//2 判断库存是否足够Integer inventoryNumber = result == null ? 0 : Integer.parseInt(result);//3 扣减库存if(inventoryNumber > 0) {stringRedisTemplate.opsForValue().set("inventory001",String.valueOf(--inventoryNumber));retMessage = "成功卖出一个商品,库存剩余: "+inventoryNumber;System.out.println(retMessage);}else{retMessage = "商品卖完了,o(╥﹏╥)o";}}finally {stringRedisTemplate.delete(key);}}return retMessage+"\t"+"服务端口号:"+port;}
}
结果:
1、手工测试OK,使用Jmeter压测5000也OK
2、递归是一种思想没错,但是容号导致StackOverflowError,不太推荐,需进一步完善
V3.2 版本
使用多线程判断想想JUC里面的虚假唤醒,用while替代if,用自旋替代送归重试。
import cn.hutool.core.util.IdUtil;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;@Service
@Slf4j
public class InventoryService {@Autowiredprivate StringRedisTemplate stringRedisTemplate;@Value("${server.port}")private String port;private Lock lock = new ReentrantLock();public String sale() {String retMessage = "";String key = "zzyyRedisLock";String uuidValue = IdUtil.simpleUUID()+":"+Thread.currentThread().getId();while(!stringRedisTemplate.opsForValue().setIfAbsent(key, uuidValue)){//暂停20毫秒,类似CAS自旋try { TimeUnit.MILLISECONDS.sleep(20); } catch (InterruptedException e) { e.printStackTrace(); }}try {//1 查询库存信息String result = stringRedisTemplate.opsForValue().get("inventory001");//2 判断库存是否足够Integer inventoryNumber = result == null ? 0 : Integer.parseInt(result);//3 扣减库存if(inventoryNumber > 0) {stringRedisTemplate.opsForValue().set("inventory001",String.valueOf(--inventoryNumber));retMessage = "成功卖出一个商品,库存剩余: "+inventoryNumber;System.out.println(retMessage);}else{retMessage = "商品卖完了,o(╥﹏╥)o";}}finally {stringRedisTemplate.delete(key);}return retMessage+"\t"+"服务端口号:"+port;}
}
问题:部署了微服务的Java程序机器挂了,代码层面根本没有走到finallyi这块,没办法保证解锁(无过期时间该key一直存在),这个kev没有被删除,需要加入一个过期时间限定key。
V4.1 版本
......
while(!stringRedisTemplate.opsForValue().setIfAbsent(key, uuidValue)) {//暂停20毫秒,进行递归重试.....try { TimeUnit.MILLISECONDS.sleep(20); } catch (InterruptedException e) { e.printStackTrace(); }
}
......
stringRedisTemplate.expire(key,30L,TimeUnit.SECONDS);
......
结论:虽然加了过期时间,但是设置key+过期时间分开了,不具备原子性。
V4.2 版本
import cn.hutool.core.util.IdUtil;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;@Service
@Slf4j
public class InventoryService {@Autowiredprivate StringRedisTemplate stringRedisTemplate;@Value("${server.port}")private String port;private Lock lock = new ReentrantLock();public String sale() {String retMessage = "";String key = "zzyyRedisLock";String uuidValue = IdUtil.simpleUUID()+":"+Thread.currentThread().getId();while(!stringRedisTemplate.opsForValue().setIfAbsent(key, uuidValue,30L,TimeUnit.SECONDS)){//暂停毫秒try { TimeUnit.MILLISECONDS.sleep(20); } catch (InterruptedException e) { e.printStackTrace(); }}try {//1 查询库存信息String result = stringRedisTemplate.opsForValue().get("inventory001");//2 判断库存是否足够Integer inventoryNumber = result == null ? 0 : Integer.parseInt(result);//3 扣减库存if(inventoryNumber > 0) {stringRedisTemplate.opsForValue().set("inventory001",String.valueOf(--inventoryNumber));retMessage = "成功卖出一个商品,库存剩余: "+inventoryNumber;System.out.println(retMessage);}else{retMessage = "商品卖完了,o(╥﹏╥)o";}}finally {stringRedisTemplate.delete(key);}return retMessage+"\t"+"服务端口号:"+port;}
}
使用Jmeter压测OK
结论:加锁和过期时间设置必须同一行,保证原子性。
V5.0 版本
4.2版本出现的问题:实际业务处理时间如果超过了默认设晋key的过期时间怎么办??张冠李戴,别除了别人的锁(只能自己除自己的,不许动别人的)
改进:
import cn.hutool.core.util.IdUtil;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;@Service
@Slf4j
public class InventoryService {@Autowiredprivate StringRedisTemplate stringRedisTemplate;@Value("${server.port}")private String port;private Lock lock = new ReentrantLock();public String sale() {String retMessage = "";String key = "zzyyRedisLock";String uuidValue = IdUtil.simpleUUID()+":"+Thread.currentThread().getId();while(!stringRedisTemplate.opsForValue().setIfAbsent(key, uuidValue,30L,TimeUnit.SECONDS)) {//暂停毫秒try { TimeUnit.MILLISECONDS.sleep(20); } catch (InterruptedException e) { e.printStackTrace(); }}try {//1 查询库存信息String result = stringRedisTemplate.opsForValue().get("inventory001");//2 判断库存是否足够Integer inventoryNumber = result == null ? 0 : Integer.parseInt(result);//3 扣减库存if(inventoryNumber > 0) {stringRedisTemplate.opsForValue().set("inventory001",String.valueOf(--inventoryNumber));retMessage = "成功卖出一个商品,库存剩余: "+inventoryNumber+"\t"+uuidValue;System.out.println(retMessage);}else{retMessage = "商品卖完了,o(╥﹏╥)o";}}finally {// v5.0判断加锁与解锁是不是同一个客户端,同一个才行,自己只能删除自己的锁,不误删他人的if(stringRedisTemplate.opsForValue().get(key).equalsIgnoreCase(uuidValue)){stringRedisTemplate.delete(key);}}return retMessage+"\t"+"服务端口号:"+port;}
}
V6.0 版本
上面5.0版本出现的问题:finally块的判断+del删除除操作不是原子性的。
解决方案:启用lua脚本编写redis分布式锁判断+删除判断代码。
原理:Redis调用Lua本通过eval命令保证代码执行的原子性,直接用return返回脚本执行后的结果值。
Lua 脚本
官网:https://redis.io/docs/manual/patterns/distributed-locks/
脚本格式:
eval luascript numkeys [key [key ]][arg [arg ...]]
案例一:输出文字
案例二:组合命令
案例三:执行命令
案例四:条件判断
使用格式如下
eval "if redis.call('get',KEYS[1])==ARGV[1] then return redis.call('del',KEYS[1]) else return 0 end" 1 zzyyRedisLock 1111-2222-3333
解决方式
import cn.hutool.core.util.IdUtil;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.data.redis.core.script.DefaultRedisScript;
import org.springframework.stereotype.Service;import java.util.Arrays;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;@Service
@Slf4j
public class InventoryService {@Autowiredprivate StringRedisTemplate stringRedisTemplate;@Value("${server.port}")private String port;private Lock lock = new ReentrantLock();public String sale() {String retMessage = "";String key = "zzyyRedisLock";String uuidValue = IdUtil.simpleUUID()+":"+Thread.currentThread().getId();while(!stringRedisTemplate.opsForValue().setIfAbsent(key, uuidValue,30L,TimeUnit.SECONDS)) {//暂停毫秒try { TimeUnit.MILLISECONDS.sleep(20); } catch (InterruptedException e) { e.printStackTrace(); }}try {//1 查询库存信息String result = stringRedisTemplate.opsForValue().get("inventory001");//2 判断库存是否足够Integer inventoryNumber = result == null ? 0 : Integer.parseInt(result);//3 扣减库存if(inventoryNumber > 0) {stringRedisTemplate.opsForValue().set("inventory001",String.valueOf(--inventoryNumber));retMessage = "成功卖出一个商品,库存剩余: "+inventoryNumber+"\t"+uuidValue;System.out.println(retMessage);}else{retMessage = "商品卖完了,o(╥﹏╥)o";}}finally {//V6.0 将判断+删除自己的合并为lua脚本保证原子性String luaScript ="if (redis.call('get',KEYS[1]) == ARGV[1]) then " +"return redis.call('del',KEYS[1]) " +"else " +"return 0 " +"end";stringRedisTemplate.execute(new DefaultRedisScript<>(luaScript, Boolean.class), Arrays.asList(key), uuidValue);}return retMessage+"\t"+"服务端口号:"+port;}
}
BUG 说明