Mysql、Redis、Redisson分布式锁

代码

Mysql

代码

ProductEntity selectLock(@Param("title") String title);

<select id="selectLock" resultType="com.csea.lock.pojo.ProductEntity">
    select * from product where title = #{title} for update
</select>

	@RequestMapping("mysql/singleLock")
    @Transactional(rollbackFor = Exception.class)
    public String mysqlSingleLock() throws Exception {
        log.info("进入了方法");
        ProductEntity selectLock = productMapper.selectLock("苹果");
        if (StringUtils.isEmpty(selectLock)) {
            throw new Exception("没有分布式锁");
        }
        log.info("拿到了锁");

        Thread.sleep(5000);

        return "完成了";
    }

效果

启动8080，8081两个端口进行访问
5秒之后拿到了锁

Redis

原理

SET resource_name my_random_value NX PX 30000
resource_name：资源名称
my_random_value：随机值，每个线程随机值不同，用于释放锁时的校验
NX：key不存在时设置成功，反之不超过
PX：过期时间，出现异常情况，锁可以过期失效
利用NX的原子性，多个线程并发时候，只有一个线程可以设置成功；设置成功即可获得锁，继续执行后面的业务；出现异常，锁了有效期，锁就自动释放。

代码

	private final RedisTemplate redisTemplate;

    @GetMapping("/redis/lock")
    public String redisLock() {
        log.info("进入了方法");
        String key = "Csea";
        String value = UUID.randomUUID().toString();

        RedisCallback<Boolean> redisCallback = redisConnection -> {
            // 设置NX
            RedisStringCommands.SetOption setOption = RedisStringCommands.SetOption.ifAbsent();
            // 设置过期时间
            Expiration expiration = Expiration.seconds(30);
            // 序列化Key
            byte[] redisKey = redisTemplate.getKeySerializer().serialize(key);
            // 序列化Value
            byte[] redisValue = redisTemplate.getValueSerializer().serialize(value);
            // 返回 setnx操作结果
            return redisConnection.set(redisKey, redisValue, expiration, setOption);
        };

        // 获取分布式锁
        Boolean lock = (Boolean) redisTemplate.execute(redisCallback);

        if (lock) {
            log.info("拿到了锁");
            try {
                Thread.sleep(5000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                // 释放锁

                // LUA脚本
                String script = "if redis.call(\"get\", KEYS[1]) == ARGV[1] then\n" +
                        "  return redis.call(\"del\",KEYS[1])\n" +
                        "else\n" +
                        "  return 0\n" +
                        "end";
                RedisScript<Boolean> redisScript = RedisScript.of(script, Boolean.class);
                List<String> keyList = Arrays.asList(key);

                Boolean result = (Boolean) redisTemplate.execute(redisScript, keyList, value);
                log.info("释放锁结果：{}", result);
            }
        }
        log.info("执行结束");
        return "执行结束";
    }

效果

启动8080，8081两个端口进行访问
8080没有拿到锁，就直接运行结束了。

分布式下的定时任务

redis锁的代码抽离

@Slf4j
public class RedisLock implements AutoCloseable {

    private RedisTemplate redisTemplate;
    private String key;
    private String value;
    private int expireTime;

    public RedisLock(RedisTemplate redisTemplate, String key, int expireTime) {
        this.redisTemplate = redisTemplate;
        this.key = key;
        this.value = UUID.randomUUID().toString();
        this.expireTime = expireTime;
    }

    public boolean getLock() {
        RedisCallback<Boolean> redisCallback = redisConnection -> {
            // 设置NX
            RedisStringCommands.SetOption setOption = RedisStringCommands.SetOption.ifAbsent();
            // 设置过期时间
            Expiration expiration = Expiration.seconds(expireTime);
            // 序列化Key
            byte[] redisKey = redisTemplate.getKeySerializer().serialize(key);
            // 序列化Value
            byte[] redisValue = redisTemplate.getValueSerializer().serialize(value);
            // 返回 setnx操作结果
            return redisConnection.set(redisKey, redisValue, expiration, setOption);
        };

        // 获取分布式锁
        Boolean lock = (Boolean) redisTemplate.execute(redisCallback);
        return lock;
    }

    public boolean unlock() {
        // LUA脚本
        String script = "if redis.call(\"get\", KEYS[1]) == ARGV[1] then\n" +
                "  return redis.call(\"del\",KEYS[1])\n" +
                "else\n" +
                "  return 0\n" +
                "end";
        RedisScript<Boolean> redisScript = RedisScript.of(script, Boolean.class);
        List<String> keyList = Arrays.asList(key);

        Boolean result = (Boolean) redisTemplate.execute(redisScript, keyList, value);
        log.info("释放锁的结果：{}", result);
        return result;
    }

    @Override
    public void close() throws Exception {
        unlock();
    }
}

定时任务代码

@Service
@Slf4j
@RequiredArgsConstructor
public class SchedulerService {

    private final RedisTemplate redisTemplate;


    @Scheduled(cron = "0/5 * * * * ?")
    public void logInfo() {
        try (RedisLock lock = new RedisLock(redisTemplate, "Csea", 30)) {
            if (lock.getLock()) {
                log.info("打印了*************Csea*************");
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

}

效果

启动8080,8081两个端口

Redisson

官网
文档
整合SpringBoot

<dependency>
	<groupId>org.redisson</groupId>
	<artifactId>redisson-spring-boot-starter</artifactId>
	<version>3.13.1</version>
</dependency>

代码

	private final RedissonClient redissonClient;

    @GetMapping("/redisson/lock")
    public String redissonLock() {
        RLock lock = redissonClient.getLock("Csea");
        log.info("进入了方法");
        try {
            lock.lock(30, TimeUnit.SECONDS);
            log.info("拿到了锁");
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
        log.info("执行结束");
        return "执行结束";
    }

效果

启动8080,8081两个端口

JMeter压测

压测代码

@Service
@Slf4j
public class JmService {

    static Map<String, Integer> productMap = new HashMap<>(10);
    static Map<String, Integer> stockMap = new HashMap<>(10);
    static Map<String, String> orderMap = new HashMap<>();

    static {
        productMap.put("123456", 100000);
        stockMap.put("123456", 100000);
    }

    private String queryMap(String projectId) {
        return "商品限量：" + productMap.get(projectId) +
                "还剩下：" + stockMap.get(projectId) + " 份" +
                "下单用户数数量：" + orderMap.size();
    }

    public String querySecKillProductInfo(String projectId) {
        return this.queryMap(projectId);
    }


    @Autowired
    private RedissonClient redissonClient;

    public void secKillProject(String productId) {
        RLock lock = redissonClient.getLock("myLock");

        log.info("锁状态：{}", lock.isLocked());
        try {
            if (lock.isLocked()) {
                throw new RuntimeException("当前请求过多");
            }
            // 加锁
            lock.lock();

            // 如果库存为0 活动结束
            int stockNum = stockMap.get(productId);
            if (stockNum == 0) {
                throw new RuntimeException("商品已售空，活动结束");
            } else {
                // 模拟订单
                orderMap.put(String.valueOf(System.currentTimeMillis()), productId);
                // 扣库存
                stockNum -= 1;

                stockMap.put(productId, stockNum);
            }
        } catch (RuntimeException e) {
            e.printStackTrace();
        } finally {
            // 解锁
            lock.unlock();
        }
    }
}

	private final JmService jmService;

    /**
     * 利用Redisson进行秒杀压测 Demo
     *
     * @param productId
     * @return
     */
    @GetMapping("/redisson/query/{productId}")
    public String redissonQuery(@PathVariable String productId) {
        return jmService.querySecKillProductInfo(productId);
    }

    @GetMapping("/redisson/order/{productId}")
    public String redissonSkill(@PathVariable String productId) {
        jmService.secKillProject(productId);
        return jmService.querySecKillProductInfo(productId);
    }

配置

5000个线程同时访问

效果

对比

方式	优点	缺点
数据库	实现简单，易理解	数据库压力大
Redis	易理解	不支持阻塞
Redisson	提供锁的方法，可以阻塞

本文地址：https://blog.csdn.net/qq_38494341/article/details/107359544