深入解析Redis中的分布式锁
本篇文章给大家主要带大家了解一下Redis中分布式锁的实现和代码解析，希望对大家有所帮助！
Redis 分布式锁
大家项目中都会使用到分布式锁把，通常用来做数据的有序操作场景，比如一笔订单退款（如果可以退多次的情况）。或者用户多端下单。【相关推荐：Redis视频教程】
Maven 依赖
我主要是基于 Spring-Boot 2.1.2 + Jedis 进行实现
<?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>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.2.RELEASE</version>
</parent>
<groupId>cn.edu.cqvie</groupId>
<artifactId>redis-lock</artifactId>
<version>1.0-SNAPSHOT</version>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<java.version>1.8</java.version>
<redis.version>2.9.0</redis.version>
<spring-test.version>5.0.7</spring-test.version>
</properties>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-autoconfigure</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.data</groupId>
<artifactId>spring-data-redis</artifactId>
</dependency>
<dependency>
<groupId>redis.clients</groupId>
<artifactId>jedis</artifactId>
<version>${redis.version}</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-logging</artifactId>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>log4j-over-slf4j</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
</plugins>
</build>
</project>配置文件
application.properties 配置文件内容如下：
spring.redis.host=127.0.0.1 spring.redis.port=6379 spring.redis.password= spring.redis.timeout=30000 spring.redis.jedis.pool.max-active=8 spring.redis.jedis.pool.min-idle=2 spring.redis.jedis.pool.max-idle=4 logging.level.root=INFO
接口定义
接口定义，对于锁我们核心其实就连个方法 lock 和 unlock.
public interface RedisLock { long TIMEOUT_MILLIS = 30000; int RETRY_MILLIS = 30000; long SLEEP_MILLIS = 10; boolean tryLock(String key); boolean lock(String key); boolean lock(String key, long expire); boolean lock(String key, long expire, long retryTimes); boolean unlock(String key); }
分布式锁实现
我的实现方式是通过 setnx 方式实现了，如果存在 tryLock 逻辑的话，会通过 自旋 的方式重试
// AbstractRedisLock.java 抽象类 public abstract class AbstractRedisLock implements RedisLock { @Override public boolean lock(String key) { return lock(key, TIMEOUT_MILLIS); } @Override public boolean lock(String key, long expire) { return lock(key, TIMEOUT_MILLIS, RETRY_MILLIS); } } // 具体实现 @Component public class RedisLockImpl extends AbstractRedisLock { private Logger logger = LoggerFactory.getLogger(getClass()); @Autowired private RedisTemplate<String, String> redisTemplate; private ThreadLocal<String> threadLocal = new ThreadLocal<String>(); private static final String UNLOCK_LUA; static { StringBuilder sb = new StringBuilder(); sb.append("if redis.call(\"get\",KEYS[1]) == ARGV[1] "); sb.append("then "); sb.append(" return redis.call(\"del\",KEYS[1]) "); sb.append("else "); sb.append(" return 0 "); sb.append("end "); UNLOCK_LUA = sb.toString(); } @Override public boolean tryLock(String key) { return tryLock(key, TIMEOUT_MILLIS); } public boolean tryLock(String key, long expire) { try { return !StringUtils.isEmpty(redisTemplate.execute((RedisCallback<String>) connection -> { JedisCommands commands = (JedisCommands) connection.getNativeConnection(); String uuid = UUID.randomUUID().toString(); threadLocal.set(uuid); return commands.set(key, uuid, "NX", "PX", expire); })); } catch (Throwable e) { logger.error("set redis occurred an exception", e); } return false; } @Override public boolean lock(String key, long expire, long retryTimes) { boolean result = tryLock(key, expire); while (!result && retryTimes-- > 0) { try { logger.debug("lock failed, retrying...{}", retryTimes); Thread.sleep(SLEEP_MILLIS); } catch (InterruptedException e) { return false; } result = tryLock(key, expire); } return result; } @Override public boolean unlock(String key) { try { List<String> keys = Collections.singletonList(key); List<String> args = Collections.singletonList(threadLocal.get()); Long result = redisTemplate.execute((RedisCallback<Long>) connection -> { Object nativeConnection = connection.getNativeConnection(); if (nativeConnection instanceof JedisCluster) { return (Long) ((JedisCluster) nativeConnection).eval(UNLOCK_LUA, keys, args); } if (nativeConnection instanceof Jedis) { return (Long) ((Jedis) nativeConnection).eval(UNLOCK_LUA, keys, args); } return 0L; }); return result != null && result > 0; } catch (Throwable e) { logger.error("unlock occurred an exception", e); } return false; } }
测试代码
最后再来看看如何使用吧. (下面是一个模拟秒杀的场景)
@RunWith(SpringRunner.class) @SpringBootTest public class RedisLockImplTest { private Logger logger = LoggerFactory.getLogger(getClass()); @Autowired private RedisLock redisLock; @Autowired private StringRedisTemplate redisTemplate; private ExecutorService executors = Executors.newScheduledThreadPool(8); @Test public void lock() { // 初始化库存 redisTemplate.opsForValue().set("goods-seckill", "10"); List<Future> futureList = new ArrayList<>(); for (int i = 0; i < 100; i++) { futureList.add(executors.submit(this::seckill)); try { Thread.sleep(100); } catch (InterruptedException e) { e.printStackTrace(); } } // 等待结果，防止主线程退出 futureList.forEach(action -> { try { action.get(); } catch (InterruptedException | ExecutionException e) { e.printStackTrace(); } }); } public int seckill() { String key = "goods"; try { redisLock.lock(key); int num = Integer.valueOf(Objects.requireNonNull(redisTemplate.opsForValue().get("goods-seckill"))); if (num > 0) { redisTemplate.opsForValue().set("goods-seckill", String.valueOf(--num)); logger.info("秒杀成功，剩余库存：{}", num); } else { logger.error("秒杀失败，剩余库存：{}", num); } return num; } catch (Throwable e) { logger.error("seckill exception", e); } finally { redisLock.unlock(key); } return 0; } }
总结
本文是 Redis 锁的一种简单的实现方式，基于 jedis 实现了锁的重试操作。
但是缺点还是有的，不支持锁的自动续期，锁的重入，以及公平性（目前通过自旋的方式实现，相当于是非公平的方式）。
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