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本篇內(nèi)容主要講解“如何用redis來實現(xiàn)分布式鎖”，感興趣的朋友不妨來看看。本文介紹的方法操作簡單快捷，實用性強。下面就讓小編來帶大家學(xué)習(xí)“如何用redis來實現(xiàn)分布式鎖”吧!
boot_redis01
boot_redis02
<?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>2.4.4</version> <relativePath/> <!-- lookup parent from repository --> </parent> <groupId>com.lau</groupId> <artifactId>boot_redis01</artifactId> <version>0.0.1-SNAPSHOT</version> <name>boot_redis01</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-web</artifactId> </dependency> <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-actuator --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-actuator</artifactId> </dependency> <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-data-redis --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-data-redis</artifactId> </dependency> <!-- https://mvnrepository.com/artifact/org.apache.commons/commons-pool2 --> <dependency> <groupId>org.apache.commons</groupId> <artifactId>commons-pool2</artifactId> </dependency> <!-- https://mvnrepository.com/artifact/redis.clients/jedis --> <dependency> <groupId>redis.clients</groupId> <artifactId>jedis</artifactId> <version>3.1.0</version> </dependency> <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-aop --> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-aop</artifactId> </dependency> <!-- https://mvnrepository.com/artifact/org.redisson/redisson --> <dependency> <groupId>org.redisson</groupId> <artifactId>redisson</artifactId> <version>3.13.4</version> </dependency> <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>junit</groupId> <artifactId>junit</artifactId> <version>4.12</version> </dependency> </dependencies> <build> <plugins> <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> </plugin> </plugins> </build> </project>
server.port=1111 spring.redis.database=0 spring.redis.host=localhost spring.redis.port=6379 #連接池最大連接數(shù)（使用負值表示沒有限制）默認8 spring.redis.lettuce.pool.max-active=8 #連接池最大阻塞等待時間（使用負值表示沒有限制）默認-1 spring.redis.lettuce.pool.max-wait=-1 #連接池中的最大空閑連接默認8 spring.redis.lettuce.pool.max-idle=8 #連接池中的最小空閑連接默認0 spring.redis.lettuce.pool.min-idle=0 ?
package com.lau.boot_redis01;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
@SpringBootApplication(exclude= {DataSourceAutoConfiguration.class})
public class BootRedis01Application {
public static void main(String[] args) {
SpringApplication.run(BootRedis01Application.class, args);
}
}package com.lau.boot_redis01.config;
import org.redisson.Redisson;
import org.redisson.config.Config;
import org.springframework.beans.factory.annotation.Value;
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;
@Configuration
public class RedisConfig {
@Value("${spring.redis.host}")
private String redisHost;
/**
*保證不是序列化后的亂碼配置
*/
@Bean
public RedisTemplate<String, Serializable>redisTemplate(LettuceConnectionFactory connectionFactory){
RedisTemplate<String,Serializable> redisTemplate =new RedisTemplate<>();
redisTemplate.setKeySerializer(new StringRedisSerializer());
redisTemplate.setValueSerializer(new GenericJackson2JsonRedisSerializer());
redisTemplate.setConnectionFactory(connectionFactory);
return redisTemplate;
}
@Bean
public Redisson redisson(){
Config config = new Config();
config.useSingleServer().setAddress("redis://"+redisHost+":6379").setDatabase(0);
return (Redisson) Redisson.create(config);
}
}package com.lau.boot_redis01.controller;
import com.lau.boot_redis01.util.RedisUtil;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.web.bind.annotation.GetMapping;
import redis.clients.jedis.Jedis;
import java.util.Collections;
import java.util.List;
import java.util.UUID;
import java.util.concurrent.TimeUnit;
@RestController
public class GoodController {
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
private static final String REDIS_LOCK = "atguigulock";
@GetMapping("/buy_goods")
public String buy_Goods() throws Exception {
String value = UUID.randomUUID().toString() + Thread.currentThread().getName();
try{
//1、key加過期時間是因為如果redis客戶端宕機了會造成死鎖，其它客戶端永遠獲取不到鎖
//2、這里將setnx與鎖過期兩條命令合二為一，是為了解決命令分開執(zhí)行引發(fā)的原子性問題：
//setnx 中間會被其它redis客戶端命令加塞 2、expire
//3①、為了避免線程執(zhí)行業(yè)務(wù)時間大于鎖過期時間導(dǎo)致竄行操作，再釋放鎖時應(yīng)判斷是否是自己加的鎖；
//還有另外一種解決方案：鎖續(xù)期——額外開啟一個守護線程定時給當前key加超時時間（如5s到期，每2.5s ttl判斷一次，并加2.5s超時時間，不斷續(xù)期，線程將使用主動刪除key命令的方式釋放鎖；另，當此redis客戶端命令宕機后，此守護線程會自動隨之消亡，不會再主動續(xù)期——此機制使得其它redis客戶端可以獲得鎖，不會發(fā)生死鎖或長期等待）
Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(REDIS_LOCK, value, 10L, TimeUnit.SECONDS);//setnx
if(!flag){
return "獲取鎖失?。?quot;;
}
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("你已經(jīng)成功秒殺商品，此時還剩余：" + realNumber + "件"+"\t 服務(wù)器端口: "+serverPort);
return "你已經(jīng)成功秒殺商品，此時還剩余：" + realNumber + "件"+"\t 服務(wù)器端口: "+serverPort;
}
System.out.println("商品已經(jīng)售罄/活動結(jié)束/調(diào)用超時，歡迎下次光臨"+"\t 服務(wù)器端口: "+serverPort);
return "商品已經(jīng)售罄/活動結(jié)束/調(diào)用超時，歡迎下次光臨"+"\t 服務(wù)器端口: "+serverPort;
}
finally {
// if(stringRedisTemplate.opsForValue().get(REDIS_LOCK).equals(value)){
// stringRedisTemplate.delete(REDIS_LOCK);
// }
//3②這里也存在命令的原子問題：獲取當前key經(jīng)相等判斷后與刪除對應(yīng)key是兩個不同命令，中間會被加塞
//解決方法1：redis事務(wù)
// stringRedisTemplate.watch(REDIS_LOCK);
// while(true){
// if(stringRedisTemplate.opsForValue().get(REDIS_LOCK).equalsIgnoreCase(value)){
// stringRedisTemplate.setEnableTransactionSupport(true);
// stringRedisTemplate.multi();
// stringRedisTemplate.delete(REDIS_LOCK);
//
// List<Object> list = stringRedisTemplate.exec();
//
// if(list == null){
// continue;
// }
// }
//
// stringRedisTemplate.unwatch();
// break;
// }
//解決方法2：lua腳本——原子操作
Jedis jedis = RedisUtil.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), 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();
}
}
}
}
}問題：沒有加鎖，并發(fā)下數(shù)字不對，會出現(xiàn)超賣現(xiàn)象
① synchronized 不見不散
② ReentrantLock 過時不候
在單機環(huán)境下，可以使用synchronized或Lock來實現(xiàn)。 但是在分布式系統(tǒng)中，因為競爭的線程可能不在同一個節(jié)點上(同一個jvm中），所以需要一個讓所有進程都能訪問到的鎖來實現(xiàn)，比如redis或者zookeeper來構(gòu)建; 不同進程jvm層面的鎖就不管用了，那么可以利用第三方的一個組件，來獲取鎖，未獲取到鎖，則阻塞當前想要運行的線程
注：分布式部署后，單機鎖還是出現(xiàn)超賣現(xiàn)象，需要分布式鎖
啟動兩個微服務(wù)1111和2222，訪問使用：http://localhost/buy_goods(即通過nginx輪詢方式訪問1111和2222兩個微服務(wù))
nginx.conf配置
#user nobody;
worker_processes 1;
#error_log logs/error.log;
#error_log logs/error.log notice;
#error_log logs/error.log info;
#pid logs/nginx.pid;
events {
worker_connections 1024;
}
http {
include mime.types;
default_type application/octet-stream;
#log_format main '$remote_addr - $remote_user [$time_local] "$request" '
# '$status $body_bytes_sent "$http_referer" '
# '"$http_user_agent" "$http_x_forwarded_for"';
#access_log logs/access.log main;
sendfile on;
#tcp_nopush on;
#keepalive_timeout 0;
keepalive_timeout 65;
#gzip on;
upstream mynginx{#反向代理的服務(wù)器列表，權(quán)重相同，即負載均衡使用輪訓(xùn)策略
server localhost:1111 weight=1;
server localhost:2222 weight=1;
}
server {
listen 80;
server_name localhost;
#charset koi8-r;
#access_log logs/host.access.log main;
location / {
#root html;
#index index.html index.htm;
proxy_pass http://mynginx;#配置反向代理
index index.html index.htm;
}
#error_page 404 /404.html;
# redirect server error pages to the static page /50x.html
#
error_page 500 502 503 504 /50x.html;
location = /50x.html {
root html;
}
# proxy the PHP scripts to Apache listening on 127.0.0.1:80
#
#location ~ \.php$ {
# proxy_pass http://127.0.0.1;
#}
# pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
#
#location ~ \.php$ {
# root html;
# fastcgi_pass 127.0.0.1:9000;
# fastcgi_index index.php;
# fastcgi_param SCRIPT_FILENAME /scripts$fastcgi_script_name;
# include fastcgi_params;
#}
# deny access to .htaccess files, if Apache's document root
# concurs with nginx's one
#
#location ~ /\.ht {
# deny all;
#}
}
# another virtual host using mix of IP-, name-, and port-based configuration
#
#server {
# listen 8000;
# listen somename:8080;
# server_name somename alias another.alias;
# location / {
# root html;
# index index.html index.htm;
# }
#}
# HTTPS server
#
#server {
# listen 443 ssl;
# server_name localhost;
# ssl_certificate cert.pem;
# ssl_certificate_key cert.key;
# ssl_session_cache shared:SSL:1m;
# ssl_session_timeout 5m;
# ssl_ciphers HIGH:!aNULL:!MD5;
# ssl_prefer_server_ciphers on;
# location / {
# root html;
# index index.html index.htm;
# }
#}
}① 出異常的話，可能無法釋放鎖， 必須要在代碼層面finally釋放鎖
② 加鎖解鎖，lock/unlock必須同時出現(xiàn)并保證調(diào)用
① 部署了微服務(wù)jar包的機器掛了，代碼層面根本沒有走到finally這塊， 沒辦法保證解鎖，這個key沒有被刪除，需要加入一個過期時間限定key
② 需要對lockKey有過期時間的設(shè)定
① 設(shè)置key+過期時間分開了，必須要合并成一行具備原子性
① 設(shè)置鎖失效時間不合理
① 用redis自身的事務(wù)
i 未使用watch前：
ii使用watch后：
② 用Lua腳本
Redis可以通過eval命令保證代碼執(zhí)行的原子性
java配置類：
package com.lau.boot_redis01.util;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisPool;
import redis.clients.jedis.JedisPoolConfig;
public class RedisUtil {
private static JedisPool jedisPool;
static {
JedisPoolConfig jedisPoolConfig = new JedisPoolConfig();
jedisPoolConfig.setMaxTotal(20);
jedisPoolConfig.setMaxIdle(10);
jedisPool = new JedisPool(jedisPoolConfig,"127.0.0.1",6379,100000);
}
public static Jedis getJedis() throws Exception{
if (null!=jedisPool){
return jedisPool.getResource();
}
throw new Exception("Jedispool is not ok");
}
}Jedis jedis = RedisUtil.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), 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();
}
}① Redis分布式鎖如何續(xù)期? 確保redisLock過期時間大于業(yè)務(wù)執(zhí)行時間的問題（鎖續(xù)期）
② redis單點故障——redis異步復(fù)制造成的鎖丟失， 比如:主節(jié)點沒來的及把剛剛set進來這條數(shù)據(jù)給從節(jié)點，就掛了。(zk/cp、redis/ap)（redis集群）
確保redisLock過期時間大于業(yè)務(wù)執(zhí)行時間的問題；redis集群環(huán)境下，我們自己寫的也不OK, 直接上RedLock之Redisson落地實現(xiàn)
1、RedisConfig.java
@Bean
public Redisson redisson(){
Config config = new Config();
config.useSingleServer().setAddress("redis://"+redisHost+":6379").setDatabase(0);
return (Redisson) Redisson.create(config);
}2、控制器類：
package com.lau.boot_redis01.controller;
import com.lau.boot_redis01.util.RedisUtil;
import lombok.val;
import org.redisson.Redisson;
import org.redisson.RedissonLock;
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.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.UUID;
import java.util.concurrent.TimeUnit;
@RestController
public class GoodController_Redisson {
@Autowired
private StringRedisTemplate stringRedisTemplate;
@Value("${server.port}")
private String serverPort;
private static final String REDIS_LOCK = "atguigulock";
@Autowired
private Redisson redisson;
@GetMapping("/buy_goods2")
public String buy_Goods() throws Exception {
String value = UUID.randomUUID().toString() + Thread.currentThread().getName();
RLock lock = redisson.getLock(REDIS_LOCK);
try{
lock.lock();
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("你已經(jīng)成功秒殺商品，此時還剩余：" + realNumber + "件"+"\t 服務(wù)器端口: "+serverPort);
return "你已經(jīng)成功秒殺商品，此時還剩余：" + realNumber + "件"+"\t 服務(wù)器端口: "+serverPort;
}
System.out.println("商品已經(jīng)售罄/活動結(jié)束/調(diào)用超時，歡迎下次光臨"+"\t 服務(wù)器端口: "+serverPort);
return "商品已經(jīng)售罄/活動結(jié)束/調(diào)用超時，歡迎下次光臨"+"\t 服務(wù)器端口: "+serverPort;
}
finally {
//IllegalMonitorStateException:attempt unlock lock,not locked by current thread by node_id
if(lock.isLocked() && lock.isHeldByCurrentThread()){
lock.unlock();
}
}
}
}注：在并發(fā)多的時候就可能會遇到這種錯誤，可能會被重新?lián)屨?/p>
到此，相信大家對“如何用redis來實現(xiàn)分布式鎖”有了更深的了解，不妨來實際操作一番吧！這里是億速云網(wǎng)站，更多相關(guān)內(nèi)容可以進入相關(guān)頻道進行查詢，關(guān)注我們，繼續(xù)學(xué)習(xí)！
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