基于 redis 的分布式锁的实现
基于 redis 的分布式锁的实现
一:第一种加锁方式(使用 Redis 的setnx命令实现分布)(7 万并发以下没有什么大的问题)
需要解决的问题
1:代码中出现异常会导致锁一直持有.(释放锁时在 finally{}的代码块中进行,不然中间代码出现异常时会导致锁不会进行释放).
2:在系统宕机或者异常时锁一直持有(设置锁的时间).
3:设置锁的时间问题,如果设置锁的时间比执行锁中间的代码的时间小的话,会导致锁被提前释放()(解决方案使用一个 Timer去一直去检查代码是否执行完,没有就去增加锁的持有时间)
4:redis 要搭建集群环境(可能出现主服务器挂了,从服务器没有把数据同步过去导致脏数据)
@RequestMapping("deductStock")
public String deductStock(){
String redisLock = "sjf1";
String clientId = UUID.randomUUID().toString();
try {
//获取锁
Boolean a = redisTemplate.opsForValue().setIfAbsent(redisLock, clientId,10,TimeUnit.SECONDS);
//没有获取到锁直接返回
if (a == false){
return "没有抢到锁";
}
//获取库存进行判断
int stock = Integer.parseInt(redisTemplate.opsForValue().get("stock"));
if (stock > 0){
int realStock = stock - 1;
redisTemplate.opsForValue().set("stock",realStock + "");
System.out.println("扣除库存成功,剩余库存"+realStock);
return "扣除库存成功,剩余库存"+realStock + " a= " + a;
}else {
System.out.println("扣减失败,库存不足");
return "扣减失败,库存不足" + " a= " + a;
}
}finally {
if (clientId.equals(redisTemplate.opsForValue().get(redisLock))){
redisTemplate.delete(redisLock);
}
}
}
2:第二种加锁方式(redisson)(近乎完美)
1:秒杀场景下导致 Redis 压力过大(可以将库存进行分段实现分段加锁)
分段加锁可能出现一些问题(每段库存大小,这段库存不够跳到下个加锁代码段)
https://blog.csdn.net/u010391342/article/details/84372342
@RequestMapping("deductRedisStock")
public String deductRedisStock(){
String redisLock = "sjf";
//获取锁
RLock lock = redisson.getLock(redisLock);
try {
//加锁
lock.lock();
int stock = Integer.parseInt(redisTemplate.opsForValue().get("stock"));
if (stock > 0){
int realStock = stock - 1;
redisTemplate.opsForValue().set("stock",realStock + "");
System.out.println("扣除库存成功,剩余库存"+realStock);
return "扣除库存成功,剩余库存"+realStock;
}else {
System.out.println("扣减失败,库存不足");
return "扣减失败,库存不足";
}
}finally {
//释放锁
lock.unlock();
}
}
附:配置
aplication.yml 文件配置
server:
port: 8002
spring:
redis:
host: 192.168.2.9
port: 6379
password:
timeout: 1000
database: 1
pool:
max-active: 8 #最大连接数
max-idle: 8 #最大空闲连接数
max-wait: -1 #最大等待时间
min-idle: 0
#下面是 Redis 集群配置
# sentinel:
# master: master1
# nodes: 172.16.33.216:16001,172.16.33.216:16002
main:
allow-bean-definition-overriding: true
pow 文件配置
<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>4.0.0modelVersion>
<groupId>com.lockgroupId>
<artifactId>redis-lockartifactId>
<version>0.0.1-SNAPSHOTversion>
<name>redis-lockname>
<description>Demo project for Spring Bootdescription>
<packaging>warpackaging>
<parent>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starter-parentartifactId>
<version>2.1.3.RELEASEversion>
<relativePath/>
parent>
<properties>
<java.version>1.8java.version>
properties>
<dependencies>
<dependency>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starter-data-redisartifactId>
dependency>
<dependency>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starter-webartifactId>
dependency>
<dependency>
<groupId>org.redissongroupId>
<artifactId>redissonartifactId>
<version>2.2.13version>
dependency>
<dependency>
<groupId>org.projectlombokgroupId>
<artifactId>lombokartifactId>
<optional>trueoptional>
dependency>
<dependency>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-starter-testartifactId>
<scope>testscope>
<exclusions>
<exclusion>
<groupId>org.junit.vintagegroupId>
<artifactId>junit-vintage-engineartifactId>
exclusion>
exclusions>
dependency>
<dependency>
<groupId>io.projectreactorgroupId>
<artifactId>reactor-testartifactId>
<scope>testscope>
dependency>
<dependency>
<groupId>redis.clientsgroupId>
<artifactId>jedisartifactId>
<version>2.7.3version>
dependency>
<dependency>
<groupId>com.alibabagroupId>
<artifactId>fastjsonartifactId>
<version>1.2.68version>
dependency>
dependencies>
<repositories>
<repository>
<id>nexus-aliyunid>
<name>Nexus aliyunname>
<layout>defaultlayout>
<url>http://maven.aliyun.com/nexus/content/groups/publicurl>
<snapshots>
<enabled>falseenabled>
snapshots>
<releases>
<enabled>trueenabled>
releases>
repository>
repositories>
<profiles>
<profile>
<id>localid>
<properties>
<profileActive>localprofileActive>
properties>
<activation>
<activeByDefault>trueactiveByDefault>
activation>
profile>
<profile>
<id>devid>
<properties>
<profileActive>devprofileActive>
properties>
profile>
<profile>
<id>prodid>
<properties>
<profileActive>prodprofileActive>
properties>
profile>
profiles>
<build>
<plugins>
<plugin>
<groupId>org.springframework.bootgroupId>
<artifactId>spring-boot-maven-pluginartifactId>
<version>2.0.6.RELEASEversion>
<configuration>
<mainClass>com.lock.redislock.RedisLockApplicationmainClass>
<layout>ZIPlayout>
configuration>
<executions>
<execution>
<goals>
<goal>repackagegoal>
goals>
execution>
executions>
plugin>
plugins>
<resources>
<resource>
<directory>src/main/resourcesdirectory>
<filtering>truefiltering>
<includes>
<include>application-*.ymlinclude>
<include>redisson-*.ymlinclude>
<include>application.ymlinclude>
includes>
resource>
resources>
build>
project>
@Bean
public Redisson getRedisson(){
Config config = new Config();
//单机模式 依次设置redis地址和密码
config.useSingleServer().
setAddress("192.168.2.9:6379").setDatabase(1);
return (Redisson)Redisson.create(config);
}