关于分布式锁,常见的面试题如下:
- Redis除了拿来做缓存,你还见过基于Redis的什么用法?
- Redis 做分布式锁的时候有需要注意的问题?
- 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?
- 集群模式下,比如主从模式,有没有什么问题呢?
- 你知道 Redis 是怎么解决集群模式也不靠谱的问题的吗?
- 那你简单的介绍一下 Redlock 吧?你简历上写redisson,你谈谈
- 你觉得 Redlock 有什么问题呢?
- Redis分布式锁如何续期?看门狗知道吗?
锁的种类
- 单机版同一个JVM虚拟机内,synchronized或者Lock接口
- 分布式不同个JVM虚拟机内,单机的线程锁机制不再起作用,资源类在不同的服务器之间共享了。
一个靠谱分布式锁需要具备的条件和刚需如下:
- 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。
- 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。
- 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。
Redis实现分布式锁命令如下: 1.setnx key value 但是,上述差评,setnx+expire不安全,两条命令非原子性的
2.set key value [EX seconds] [PX milliseconds] [NX|XX]
Base案例(boot+redis)
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.建Module——boot_redis01和boot_redis02。
2.改POM,如下:
<?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>2.3.10.RELEASE</version>
<relativePath/>
</parent>
<groupId>com.atguigu.redis</groupId>
<artifactId>boot_redis01</artifactId>
<version>0.0.1-SNAPSHOT</version>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<!--guava-->
<dependency>
<groupId>com.google.guava</groupId>
<artifactId>guava</artifactId>
<version>23.0</version>
</dependency>
<!--web+actuator-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</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>
<!-- jedis -->
<dependency>
<groupId>redis.clients</groupId>
<artifactId>jedis</artifactId>
<version>3.1.0</version>
</dependency>
<!-- springboot-aop 技术-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-aop</artifactId>
</dependency>
<!-- redisson -->
<dependency>
<groupId>org.redisson</groupId>
<artifactId>redisson</artifactId>
<version>3.13.4</version>
</dependency>
<!--一般通用基础配置-->
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-devtools</artifactId>
<scope>runtime</scope>
<optional>true</optional>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</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>
3.写YML,如下:
# 端口号
server.port=1111
# ========================redis相关配置=====================
# Redis数据库索引(默认为0)
spring.redis.database=0
# Redis服务器地址
spring.redis.host=192.168.111.140
# Redis服务器连接端口
spring.redis.port=6379
# Redis服务器连接密码(默认为空)
spring.redis.password=
# 连接池最大连接数(使用负值表示没有限制) 默认 8
spring.redis.lettuce.pool.max-active=8
# 连接池最大阻塞等待时间(使用负值表示没有限制) 默认 -1
spring.redis.lettuce.pool.max-wait=-1
# 连接池中的最大空闲连接 默认 8
spring.redis.lettuce.pool.max-idle=8
# 连接池中的最小空闲连接 默认 0
spring.redis.lettuce.pool.min-idle=0
4.主启动,如下:
package com.atguigu.redis;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class BootRedis01Application
{
public static void main(String[] args)
{
SpringApplication.run(BootRedis01Application.class, args);
}
}
5.业务类 config配置代码如下:
package com.zzyy.study.config;
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;
import java.io.Serializable;
/**
* @auther zzyy
* @create 2020-09-15 14:47
*/
@Configuration
public class RedisConfig {
@Bean
public RedisTemplate<String, Serializable> redisTemplate(LettuceConnectionFactory connectionFactory)
{
RedisTemplate<String, Serializable> redisTemplate = new RedisTemplate<>();
redisTemplate.setKeySerializer(new StringRedisSerializer());
redisTemplate.setValueSerializer(new GenericJackson2JsonRedisSerializer());
redisTemplate.setConnectionFactory(connectionFactory);
return redisTemplate;
}
}
controller代码如下:
package com.zzyy.study.controller;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@GetMapping("/buy_goods")
public String buy_Goods()
{
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
}
}
6.小测试,结果如下:
大家来找茬
1.没有加锁,并发下数字不对,出现超卖现象,即单机版没加锁。 加synchronized或者加ReentrantLock都是可以的,但是加ReentrantLock可以设置过时不候(尝试获取锁,获取不到,就不等了,不会阻塞),而synchronized是不见不散(尝试获取不到锁,就会阻塞)。
修改之后的代码如下:
package com.zzyy.study.controller;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
@Autowired
private StringRedisTemplate stringRedisTemplate;
private final Lock lock = new ReentrantLock();
@GetMapping("/buy_goods")
public String buyGoods() throws InterruptedException
{
/*synchronized (this)
{
String number = stringRedisTemplate.opsForValue().get("goods:001");
int realNumber = number == null ? 0 : Integer.parseInt(number);
if(realNumber > 0)
{
realNumber = realNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",String.valueOf(realNumber));
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件";
}
}*/
//if (lock.tryLock(2L,TimeUnit.SECONDS))
if (lock.tryLock())
{
try
{
String number = stringRedisTemplate.opsForValue().get("goods:001");
int realNumber = number == null ? 0 : Integer.parseInt(number);
if(realNumber > 0)
{
realNumber = realNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",String.valueOf(realNumber));
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件";
}
}finally {
lock.unlock();
}
}
return "商品售罄/活动结束,欢迎下次光临";
}
}
但是因为阳哥为了上课方便演示,就用了synchronized,代码如下:
package com.zzyy.study.controller;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@GetMapping("/buy_goods")
public String buy_Goods()
{
synchronized (this) {
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
}
}
}
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。
2.分布式部署后,单机锁还是出现超卖现象,需要分布式锁。
搭建nginx分布式微服务架构,Nginx配置负载均衡,进入/usr/local/nginx/conf目录,修改nginx.conf配置文件,如下: 如果之前启动过Nginx,修改完上一步配置后请重启,/usr/local/nginx/sbin目录下执行如下命令:./nginx -s reload。
关于nginx的基础命令如下:
- 启动:./nginx
- 关闭:./nginx -s stop
- 重启:./nginx -s reload
接着启动两个微服务,通过Nginx访问,反向代理+负载均衡,nginx的IP地址/buy_goods,可以点击看到效果,一边一个,默认轮询。
上面手点,下面高并发模拟,线程组配置如下: http请求配置如下: jmeter压测结果出现了超卖线象,如下图所示 解决:上redis分布式锁setnx,官网地址:redis.io/commands/se… 修改为3.0版,如下:
package com.zzyy.study.controller;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@GetMapping("/buy_goods")
public String buy_Goods()
{
String key = "zzyyRedisLock";
String value = UUID.randomUUID().toString()+Thread.currentThread().getName();
Boolean flagLock = stringRedisTemplate.opsForValue().setIfAbsent(key, value);
if(!flagLock)
{
return "抢夺锁失败,o(╥﹏╥)o";
}
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
stringRedisTemplate.delete(key);
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
}
}
3.finally必须关闭锁资源,出异常的话,可能无法释放锁,必须要在代码层面finally释放锁。
解决:加锁解锁,lock/unlock必须同时出现并保证调用。
修改为4.0版,如下:
package com.zzyy.study.controller;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@GetMapping("/buy_goods")
public String buy_Goods()
{
String key = "zzyyRedisLock";
String value = UUID.randomUUID().toString()+Thread.currentThread().getName();
try {
Boolean flagLock = stringRedisTemplate.opsForValue().setIfAbsent(key, value);
if(!flagLock)
{
return "抢锁失败,o(╥﹏╥)o";
}
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
} finally {
stringRedisTemplate.delete(key);
}
}
}
4.部署了微服务jar包的机器挂了,代码层面根本没有走到finally这块,没办法保证解锁,这个key没有被删除,需要加入一个过期时间限定key。
代码修改5.0版本,如下:
package com.zzyy.study.controller;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@GetMapping("/buy_goods")
public String buy_Goods()
{
String key = "zzyyRedisLock";
String value = UUID.randomUUID().toString()+Thread.currentThread().getName();
try {
Boolean flagLock = stringRedisTemplate.opsForValue().setIfAbsent(key, value);
stringRedisTemplate.expire(key,10L,TimeUnit.SECONDS);
if(!flagLock)
{
return "抢锁失败,o(╥﹏╥)o";
}
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
} finally {
stringRedisTemplate.delete(key);
}
}
}
5.设置key+过期时间分开了,必须要合并成一行具备原子性。
修改为6.0版,如下:
package com.zzyy.study.controller;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@GetMapping("/buy_goods")
public String buy_Goods()
{
String key = "zzyyRedisLock";
String value = UUID.randomUUID().toString()+Thread.currentThread().getName();
try {
Boolean flagLock = stringRedisTemplate.opsForValue().setIfAbsent(key,value,10L,TimeUnit.SECONDS);
if(!flagLock)
{
return "抢锁失败,o(╥﹏╥)o";
}
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
} finally {
stringRedisTemplate.delete(key);
}
}
}
6.张冠李戴,删除了别人的锁。 解决:只能自己删除自己的,不许动别人的。
修改为7.0版,如下:
package com.zzyy.study.controller;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@GetMapping("/buy_goods")
public String buy_Goods()
{
String key = "zzyyRedisLock";
String value = UUID.randomUUID().toString()+Thread.currentThread().getName();
try {
Boolean flagLock = stringRedisTemplate.opsForValue().setIfAbsent(key,value,10L,TimeUnit.SECONDS);
if(!flagLock)
{
return "抢锁失败,o(╥﹏╥)o";
}
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
} finally {
if (stringRedisTemplate.opsForValue().get(key).equals(value)) {
stringRedisTemplate.delete(key);
}
}
}
}
7.finally块的判断+del删除操作不是原子性的。
package com.zzyy.study.controller;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@GetMapping("/buy_goods")
public String buy_Goods()
{
String key = "zzyyRedisLock";
String value = UUID.randomUUID().toString()+Thread.currentThread().getName();
try {
Boolean flagLock = stringRedisTemplate.opsForValue().setIfAbsent(key,value,10L,TimeUnit.SECONDS);
if(!flagLock)
{
return "抢锁失败,o(╥﹏╥)o";
}
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
} finally {
// 判断加锁与解锁是不是同一个客户端,他们不是同一个原子操作
if (stringRedisTemplate.opsForValue().get(key).equals(value)) {
stringRedisTemplate.delete(key);
}
}
}
}
解决:Redis调用Lua脚本通过eval命令保证代码执行的原子性
修改为8.0版,RedisUtils代码如下:
package com.zzyy.study.util;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.script.DefaultRedisScript;
import org.springframework.data.redis.serializer.RedisSerializer;
import org.springframework.data.redis.serializer.StringRedisSerializer;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;
import javax.annotation.PostConstruct;
/**
* @auther zzyy
* @create 2020-09-20 16:44
*/
public class RedisUtils
{
private static JedisPool jedisPool;
static {
JedisPoolConfig jedisPoolConfig=new JedisPoolConfig();
jedisPoolConfig.setMaxTotal(20);
jedisPoolConfig.setMaxIdle(10);
jedisPool=new JedisPool(jedisPoolConfig,"192.168.111.147",6379);
}
public static Jedis getJedis() throws Exception {
if(null!=jedisPool){
return jedisPool.getResource();
}
throw new Exception("Jedispool was not init");
}
}
修改为8.0版code,如下:
package com.zzyy.study.controller;
import com.zzyy.study.util.RedisUtils;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import redis.clients.jedis.Jedis;
import java.util.Collections;
import java.util.List;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
public static final String REDIS_LOCK_KEY = "redisLockPay";
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@GetMapping("/buy_goods")
public String buy_Goods()
{
String value = UUID.randomUUID().toString()+Thread.currentThread().getName();
try {
Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(REDIS_LOCK_KEY, value,30L,TimeUnit.SECONDS);
if(!flag)
{
return "抢夺锁失败,请下次尝试";
}
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
} finally {
Jedis jedis = RedisUtils.getJedis();
String script = "if redis.call('get', KEYS[1]) == ARGV[1] " +
"then " +
"return redis.call('del', KEYS[1]) " +
"else " +
" return 0 " +
"end";
try {
Object result = jedis.eval(script, Collections.singletonList(REDIS_LOCK_KEY), Collections.singletonList(value));
if ("1".equals(result.toString())) {
System.out.println("------del REDIS_LOCK_KEY success");
}else{
System.out.println("------del REDIS_LOCK_KEY error");
}
} finally {
if(null != jedis) {
jedis.close();
}
}
}
}
}
8.确保redisLock过期时间大于业务执行时间的问题,Redis分布式锁如何续期?
集群+CAPredis对比zookeeper如下: ①.Redis单机是CP集群是AP,对于Redis集群,redis异步复制造成的锁丢失,比如:主节点没来的及把刚刚set进来这条数据给从节点,master就挂了,从机上位但从机上无该数据 ②.Zookeeper集群的CAP 顺便复习Eureka集群注册中心的CAP,Eureka也是AP 9.综合上述,redis集群环境下,我们自己写的也不OK,直接上RedLock之Redisson落地实现。
RedisConfig配置代码如下:
package com.zzyy.study.config;
import org.redisson.Redisson;
import org.redisson.api.RedissonClient;
import org.redisson.config.Config;
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;
import java.io.Serializable;
/**
* @auther zzyy
* @create 2020-09-15 14:47
*/
@Configuration
public class RedisConfig {
@Bean
public RedisTemplate<String, Serializable> redisTemplate(LettuceConnectionFactory connectionFactory)
{
RedisTemplate<String, Serializable> redisTemplate = new RedisTemplate<>();
redisTemplate.setKeySerializer(new StringRedisSerializer());
redisTemplate.setValueSerializer(new GenericJackson2JsonRedisSerializer());
redisTemplate.setConnectionFactory(connectionFactory);
return redisTemplate;
}
@Bean
public Redisson redisson()
{
Config config = new Config();
config.useSingleServer().setAddress("redis://192.168.111.140:6379").setDatabase(0);
return (Redisson) Redisson.create(config);
}
}
业务代码修改为9.0版,如下:
package com.zzyy.study.controller;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@Autowired
private Redisson redisson;
@GetMapping("/buy_goods")
public String buy_Goods(){
String key = "zzyyRedisLock";
RLock redissonLock = redisson.getLock(key);
redissonLock.lock();
try{
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
}finally {
redissonLock.unlock();
}
}
}
官网说明,两个地址分别是redis.io/topics/dist…和redisson.org/
但是上述代码在解锁的地方还有一个Bug,就是解锁时需要判断现在还是锁定状态并且持有锁的线程还是当前线程,也是避免张冠李戴,避免解除的是别人的锁。否则抛出如下异常 业务代码修改为9.1版,如下:
package com.zzyy.study.controller;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@Autowired
private Redisson redisson;
@GetMapping("/buy_goods")
public String buy_Goods()
{
String key = "zzyyRedisLock";
RLock redissonLock = redisson.getLock(key);
redissonLock.lock();
try
{
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
}finally {
if(redissonLock.isLocked() && redissonLock.isHeldByCurrentThread())
{
redissonLock.unlock();
}
}
}
}
总结
- synchronized单机版OK,上分布式
- nginx分布式微服务,单机锁不行/(ㄒoㄒ)/~~
- 取消单机锁,上redis分布式锁setnx
- 只加了锁,没有释放锁,出异常的话,可能无法释放锁,必须要在代码层面finally释放锁
- 宕机了,部署了微服务代码层面根本没有走到finally这块,没办法保证解锁,这个key没有被删除,需要有lockKey的过期时间设定
- 为redis的分布式锁key,增加过期时间,此外,还必须要setnx+过期时间必须同一行。
- 必须规定只能自己删除自己的锁,你不能把别人的锁删除了,防止张冠李戴,1删2,2删3
- redis集群环境下,我们自己写的也不OK,直接上RedLock之Redisson落地实现
Redlock算法
官网说明,如下图所示 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)。Redis分布式锁比较正确的姿势是采用redisson这个客户端工具。
天上飞的理念(RedLock)必然有落地的实现(Redisson),地址:redis.cn/topics/dist…
单机案例
三个重要元素如下:
- 加锁:加锁实际上就是在redis中,给Key键设置一个值,为避免死锁,并给定一个过期时间
- 解锁:将Key键删除。但也不能乱删,不能说客户端1的请求将客户端2的锁给删除掉,只能自己删除自己的锁。为了保证解锁操作的原子性,我们用LUA脚本完成这一操作。先判断当前锁的字符串是否与传入的值相等,是的话就删除Key,解锁成功。
- 超时:锁key要注意过期时间,不能长期占用
面试中回答的主要考点 1.加锁关键逻辑 2.解锁关键逻辑 上面一般中小公司,不是高并发场景,是可以使用的。单机redis小业务也撑得住。单机模式中,一般都是用set/setnx+lua脚本搞定,想想它的缺点是什么?
多机案例
基于setnx的分布式锁有什么缺点? 我们加的是排它独占锁,同一时间只能有一个建redis锁成功并持有锁,严禁出现2个以上的请求线程拿到锁。危险的
Redis也提供了Redlock算法,用来实现基于多个实例的分布式锁。
锁变量由多个实例维护,即使有实例发生了故障,锁变量仍然是存在的,客户端还是可以完成锁操作。Redlock算法是实现高可靠分布式锁的一种有效解决方案,可以在实际开发中使用。 Redlock算法设计理念如下: 该方案也是基于(set 加锁、Lua 脚本解锁)进行改良的,所以redis之父antirez 只描述了差异的地方,大致方案如下。
假设我们有N个Redis主节点,例如 N = 5这些节点是完全独立的,我们不使用复制或任何其他隐式协调系统,
为了取到锁客户端执行以下操作: 该方案为了解决数据不一致的问题,直接舍弃了异步复制只使用 master 节点,同时由于舍弃了 slave,为了保证可用性,引入了 N 个节点,官方建议是 5。阳哥本次教学演示用3台实例来做说明。
客户端只有在满足下面的这两个条件时,才能认为是加锁成功。
- 条件1:客户端从超过半数(大于等于N/2+1)的Redis实例上成功获取到了锁;
- 条件2:客户端获取锁的总耗时没有超过锁的有效时间。
解决方案如下: 为什么是奇数? N = 2X + 1 (N是最终部署机器数,X是容错机器数) 案例 1.docker走起3台redis的master机器,本次设置3台master各自独立无从属关系。 进入上一步刚启动的redis容器实例,如下图所示
2.建Module,redis_redlock
3.改POM,如下:
<?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>2.3.10.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>com.atguigu.redis.redlock</groupId>
<artifactId>redis_redlock</artifactId>
<version>0.0.1-SNAPSHOT</version>
<properties>
<java.version>1.8</java.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.redisson</groupId>
<artifactId>redisson</artifactId>
<!--<version>3.12.0</version>-->
<version>3.13.4</version>
</dependency>
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<version>1.18.8</version>
</dependency>
<!--swagger-->
<dependency>
<groupId>io.springfox</groupId>
<artifactId>springfox-swagger2</artifactId>
<version>2.9.2</version>
</dependency>
<!--swagger-ui-->
<dependency>
<groupId>io.springfox</groupId>
<artifactId>springfox-swagger-ui</artifactId>
<version>2.9.2</version>
</dependency>
<dependency>
<groupId>org.apache.commons</groupId>
<artifactId>commons-lang3</artifactId>
<version>3.4</version>
<scope>compile</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>
4.写YML,如下:
spring.application.name=spring-boot-redis
server.port=9090
spring.swagger2.enabled=true
spring.redis.database=0
spring.redis.password=
spring.redis.timeout=3000
#sentinel/cluster/single
spring.redis.mode=single
spring.redis.pool.conn-timeout=3000
spring.redis.pool.so-timeout=3000
spring.redis.pool.size=10
spring.redis.single.address1=192.168.111.147:6381
spring.redis.single.address2=192.168.111.147:6382
spring.redis.single.address3=192.168.111.147:6383
5.主启动。如下:
package com.atguigu.redis.redlock;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
@SpringBootApplication
public class RedisRedlockApplication
{
public static void main(String[] args)
{
SpringApplication.run(RedisRedlockApplication.class, args);
}
}
6.业务类 CacheConfiguration配置如下:
package com.atguigu.redis.redlock.config;
import org.apache.commons.lang3.StringUtils;
import org.redisson.Redisson;
import org.redisson.api.RedissonClient;
import org.redisson.config.*;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnExpression;
import org.springframework.boot.autoconfigure.condition.ConditionalOnProperty;
import org.springframework.boot.context.properties.EnableConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
@Configuration
@EnableConfigurationProperties(RedisProperties.class)
public class CacheConfiguration {
@Autowired
RedisProperties redisProperties;
@Bean
RedissonClient redissonClient1() {
Config config = new Config();
String node = redisProperties.getSingle().getAddress1();
node = node.startsWith("redis://") ? node : "redis://" + node;
SingleServerConfig serverConfig = config.useSingleServer()
.setAddress(node)
.setTimeout(redisProperties.getPool().getConnTimeout())
.setConnectionPoolSize(redisProperties.getPool().getSize())
.setConnectionMinimumIdleSize(redisProperties.getPool().getMinIdle());
if (StringUtils.isNotBlank(redisProperties.getPassword())) {
serverConfig.setPassword(redisProperties.getPassword());
}
return Redisson.create(config);
}
@Bean
RedissonClient redissonClient2() {
Config config = new Config();
String node = redisProperties.getSingle().getAddress2();
node = node.startsWith("redis://") ? node : "redis://" + node;
SingleServerConfig serverConfig = config.useSingleServer()
.setAddress(node)
.setTimeout(redisProperties.getPool().getConnTimeout())
.setConnectionPoolSize(redisProperties.getPool().getSize())
.setConnectionMinimumIdleSize(redisProperties.getPool().getMinIdle());
if (StringUtils.isNotBlank(redisProperties.getPassword())) {
serverConfig.setPassword(redisProperties.getPassword());
}
return Redisson.create(config);
}
@Bean
RedissonClient redissonClient3() {
Config config = new Config();
String node = redisProperties.getSingle().getAddress3();
node = node.startsWith("redis://") ? node : "redis://" + node;
SingleServerConfig serverConfig = config.useSingleServer()
.setAddress(node)
.setTimeout(redisProperties.getPool().getConnTimeout())
.setConnectionPoolSize(redisProperties.getPool().getSize())
.setConnectionMinimumIdleSize(redisProperties.getPool().getMinIdle());
if (StringUtils.isNotBlank(redisProperties.getPassword())) {
serverConfig.setPassword(redisProperties.getPassword());
}
return Redisson.create(config);
}
/**
* 单机
* @return
*/
/*@Bean
public Redisson redisson()
{
Config config = new Config();
config.useSingleServer().setAddress("redis://192.168.111.147:6379").setDatabase(0);
return (Redisson) Redisson.create(config);
}*/
}
RedisPoolProperties配置如下:
package com.atguigu.redis.redlock.config;
import lombok.Data;
@Data
public class RedisPoolProperties {
private int maxIdle;
private int minIdle;
private int maxActive;
private int maxWait;
private int connTimeout;
private int soTimeout;
/**
* 池大小
*/
private int size;
}
RedisProperties如下:
package com.atguigu.redis.redlock.config;
import lombok.Data;
import lombok.ToString;
import org.springframework.boot.context.properties.ConfigurationProperties;
@ConfigurationProperties(prefix = "spring.redis", ignoreUnknownFields = false)
@Data
public class RedisProperties {
private int database;
/**
* 等待节点回复命令的时间。该时间从命令发送成功时开始计时
*/
private int timeout;
private String password;
private String mode;
/**
* 池配置
*/
private RedisPoolProperties pool;
/**
* 单机信息配置
*/
private RedisSingleProperties single;
}
RedisSingleProperties如下:
package com.atguigu.redis.redlock.config;
import lombok.Data;
@Data
public class RedisSingleProperties {
private String address1;
private String address2;
private String address3;
}
controller代码如下:
package com.atguigu.redis.redlock.controller;
import lombok.extern.slf4j.Slf4j;
import org.redisson.Redisson;
import org.redisson.RedissonRedLock;
import org.redisson.api.RLock;
import org.redisson.api.RedissonClient;
import org.redisson.config.Config;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.concurrent.TimeUnit;
@RestController
@Slf4j
public class RedLockController {
public static final String CACHE_KEY_REDLOCK = "ZZYY_REDLOCK";
@Autowired
RedissonClient redissonClient1;
@Autowired
RedissonClient redissonClient2;
@Autowired
RedissonClient redissonClient3;
@GetMapping(value = "/redlock")
public void getlock() {
//CACHE_KEY_REDLOCK为redis 分布式锁的key
RLock lock1 = redissonClient1.getLock(CACHE_KEY_REDLOCK);
RLock lock2 = redissonClient2.getLock(CACHE_KEY_REDLOCK);
RLock lock3 = redissonClient3.getLock(CACHE_KEY_REDLOCK);
RedissonRedLock redLock = new RedissonRedLock(lock1, lock2, lock3);
boolean isLock;
try {
//waitTime 锁的等待时间处理,正常情况下 等5s
//leaseTime就是redis key的过期时间,正常情况下等5分钟。
isLock = redLock.tryLock(5, 300, TimeUnit.SECONDS);
log.info("线程{},是否拿到锁:{} ",Thread.currentThread().getName(),isLock);
if (isLock) {
//TODO if get lock success, do something;
//暂停20秒钟线程
try { TimeUnit.SECONDS.sleep(20); } catch (InterruptedException e) { e.printStackTrace(); }
}
} catch (Exception e) {
log.error("redlock exception ",e);
} finally {
// 无论如何, 最后都要解锁
redLock.unlock();
System.out.println(Thread.currentThread().getName()+"\t"+"redLock.unlock()");
}
}
}
7.测试 http://localhost:9090/redlock
Redisson源码解析
简单代码如下:
package com.atguigu.redis.test;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.redisson.config.Config;
import java.util.concurrent.TimeUnit;
/**
* @auther zzyy
* @create 2021-05-06 18:23
*/
public class WatchDogDemo
{
public static final String LOCKKEY = "AAA";
private static Config config;
private static Redisson redisson;
static {
config = new Config();
config.useSingleServer().setAddress("redis://"+"192.168.111.147"+":6379").setDatabase(0);
redisson = (Redisson)Redisson.create(config);
}
public static void main(String[] args)
{
RLock redissonLock = redisson.getLock(LOCKKEY);
redissonLock.lock();
try
{
System.out.println("1111");
//暂停几秒钟线程
try { TimeUnit.SECONDS.sleep(25); } catch (InterruptedException e) { e.printStackTrace(); }
}catch (Exception e){
e.printStackTrace();
}finally {
redissonLock.unlock();
}
System.out.println(Thread.currentThread().getName() + " main ------ ends.");
//暂停几秒钟线程
try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); }
redisson.shutdown();
}
}
还记得之前说过的缓存续命吗?Redis 分布式锁过期了,但是业务逻辑还没处理完怎么办?
守护线程“续命”:额外起一个线程,定期检查线程是否还持有锁,如果有则延长过期时间。Redisson 里面就实现了这个方案,使用“看门狗”定期检查(每1/3的锁时间检查1次),如果线程还持有锁,则刷新过期时间;
那你知道redis之父设计的这个方案,还有bug吗? 1.分布式难以避免的,系统时钟影响
2.如果线程 1 从 3 个实例获取到了锁。但是这 3 个实例中的某个实例的系统时间走的稍微快一点,则它持有的锁会提前过期被释放,当他释放后,此时又有 3 个实例是空闲的,则线程2也可以获取到锁,则可能出现两个线程同时持有锁了。
在获取锁成功后,给锁加一个 watchdog,watchdog 会起一个定时任务,在锁没有被释放且快要过期的时候会续期。 缓存续命 上述源码分析1:通过redisson新建出来的锁key,默认是30秒
上述源码分析2 上述源码分析3:
watch dog自动延期机制:客户端A加锁成功,就会启动一个watch dog看门狗,他是一个后台线程,会每隔10秒检查一下,如果客户端A还持有锁key,那么就会不断的延长锁key的生存时间,默认每次续命又从30秒新开始。 上述源码分析4 流程解释如下:
- 通过exists判断,如果锁不存在,则设置值和过期时间,加锁成功
- 通过hexists判断,如果锁已存在,并且锁的是当前线程,则证明是重入锁,加锁成功
- 如果锁已存在,但锁的不是当前线程,则证明有其他线程持有锁。 返回当前锁的过期时间(代表了lockzzyy这个锁key的剩余生存时间),加锁失败
加锁查看,如下:
package com.atguigu.redis.test;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.redisson.config.Config;
import java.util.concurrent.TimeUnit;
/**
* @auther zzyy
* @create 2021-05-06 18:23
*/
public class WatchDogDemo
{
public static final String LOCKKEY = "AAA";
private static Config config;
private static Redisson redisson;
static {
config = new Config();
config.useSingleServer().setAddress("redis://"+"192.168.111.147"+":6379").setDatabase(0);
redisson = (Redisson)Redisson.create(config);
}
public static void main(String[] args)
{
RLock redissonLock = redisson.getLock(LOCKKEY);
redissonLock.lock();
try
{
System.out.println("1111");
//暂停几秒钟线程
try { TimeUnit.SECONDS.sleep(25); } catch (InterruptedException e) { e.printStackTrace(); }
}catch (Exception e){
e.printStackTrace();
}finally {
if (redissonLock.isLocked() && redissonLock.isHeldByCurrentThread()) {
redissonLock.unlock();
}
}
System.out.println(Thread.currentThread().getName() + " main ------ ends.");
//暂停几秒钟线程
try { TimeUnit.SECONDS.sleep(3); } catch (InterruptedException e) { e.printStackTrace(); }
redisson.shutdown();
}
}
可重入锁查看 ttl续命的演示:加大业务逻辑处理时间,看超过10秒钟后,redisson的续命加时。
解锁源码如下: 常见异常情况 修改如下:
package com.zzyy.study.controller;
import com.zzyy.study.util.RedisUtils;
import org.redisson.Redisson;
import org.redisson.api.RLock;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.io.ClassPathResource;
import org.springframework.core.io.support.EncodedResource;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.data.redis.core.script.RedisScript;
import org.springframework.util.FileCopyUtils;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;
import redis.clients.jedis.Jedis;
import java.io.IOException;
import java.util.Collections;
import java.util.List;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import org.springframework.core.io.support.EncodedResource;
/**
* @auther zzyy
* @create 2020-09-15 14:48
*/
@RestController
public class GoodController
{
public static final String REDIS_LOCK_KEY = "lockzzyy";
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
@Autowired
private Redisson redisson;
@GetMapping("/buy_goods")
public String buy_Goods() throws IOException
{
RLock redissonLock = redisson.getLock(REDIS_LOCK_KEY);
redissonLock.lock();
try
{
String result = stringRedisTemplate.opsForValue().get("goods:001");
int goodsNumber = result == null ? 0 : Integer.parseInt(result);
if(goodsNumber > 0)
{
int realNumber = goodsNumber - 1;
stringRedisTemplate.opsForValue().set("goods:001",realNumber + "");
System.out.println("你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort);
//暂停几秒钟线程
try { TimeUnit.SECONDS.sleep(5); } catch (InterruptedException e) { e.printStackTrace(); }
return "你已经成功秒杀商品,此时还剩余:" + realNumber + "件"+"\t 服务器端口:"+serverPort;
}else{
System.out.println("商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort);
}
return "商品已经售罄/活动结束/调用超时,欢迎下次光临"+"\t 服务器端口:"+serverPort;
}finally {
if(redissonLock.isLocked() && redissonLock.isHeldByCurrentThread())
{
redissonLock.unlock();
}
}
}
}