Redisson解决Redis分布式锁提前释放问题

项目场景:

问题描述:

原因分析:

解决方案:

思考: 

Redisson简单配置:

使用样例:

Redisson之RedissonLock源码分析

总结:


项目场景:

     分布式业务场景

问题描述:

      某天线上出现数据重复处理问题,发现是单次处理时间较长,redis分布式锁提前释放导致相同请求并发处理


原因分析:

      项目采用较简单的自定义redis分布式锁,为避免死锁定义默认过期时间10s,如下:

    override fun lock() {

        while (true) {
            //尝试获取锁
            if (tryLock()) {
                return
            }
            try {
                Thread.sleep(10)
            } catch (e: InterruptedException) {
                e.printStackTrace()
            }

        }
    }

    override fun tryLock(): Boolean {
        val value = getUniqueSign() // 随机串
        val flag = redisTemplate!!.opsForValue().setIfAbsent(name, value, 10000, TimeUnit.MILLISECONDS)
        if (flag != null && flag) {
            VALUE_lOCAL.set(value)
            INTO_NUM_LOCAL.set(if (INTO_NUM_LOCAL.get() != null) INTO_NUM_LOCAL.get() + 1 else 1)
            return true
        }
        return false
    }

缺乏对锁自动续期等实现


解决方案:

思考: 

      针对这种场景,可以考虑的是如何给锁自动续期-当业务没有执行结束的情况下,当然也可以自定义实现 比如开一个后台线程定时的给这些拿到锁的线程续期

      Redisson也正是基于这种思路实现自动续期的分布式锁,各种异常情况也考虑的更加完善,综合考虑采用Redisson的分布式锁解决方案优化

Redisson简单配置:

@Configuration
@EnableConfigurationProperties(RedissonProperties::class)
class RedissonConfig {

    @Bean
    fun redissonClient(redissonProperties: RedissonProperties): RedissonClient {
        val config = Config()
        val singleServerConfig = redissonProperties.singleServerConfig!!
        config.useSingleServer().setAddress(singleServerConfig.address)
                .setDatabase(singleServerConfig.database)
                .setUsername(singleServerConfig.username)
                .setPassword(singleServerConfig.password)
                .setConnectionPoolSize(singleServerConfig.connectionPoolSize)
              .setConnectionMinimumIdleSize(singleServerConfig.connectionMinimumIdleSize)
                .setConnectTimeout(singleServerConfig.connectTimeout)
                .setIdleConnectionTimeout(singleServerConfig.idleConnectionTimeout)
                .setRetryInterval(singleServerConfig.retryInterval)
                .setRetryAttempts(singleServerConfig.retryAttempts)
                .setTimeout(singleServerConfig.timeout)
        return Redisson.create(config)
    }

}

@ConfigurationProperties(prefix = "xxx.redisson")
class RedissonProperties {
    var singleServerConfig: SingleServerConfig? = null
}

   Redis服务使用的腾讯云的哨兵模式架构,此架构对外开放一个代理地址访问,因此这里配置单机模式配置即可;如果你是自己搭建的redis哨兵模式架构,需要按照文档配置相关必要参数

使用样例:

    ...
  
    @Autowired
    lateinit var redissonClient: RedissonClient

 
    ... 

    fun xxx() {

      ...

      val lock = redissonClient.getLock("mylock")
      lock.lock()
      try {
        
        ... 

      } finally {
        lock.unlock()
      }

        ...

    }

  使用方式和JDK提供的锁是不是很像?是不是很简单?正是Redisson这类优秀的开源产品的出现,才让我们将更多的时间投入到业务开发中...


Redisson之RedissonLock源码分析

1、lock加锁操作

    @Override
    public void lock() {
        try {
            lock(-1, null, false);
        } catch (InterruptedException e) {
            throw new IllegalStateException();
        }
    }



    // 租约期限, 也就是expire时间, -1代表未设置 将使用系统默认的30s
    private void lock(long leaseTime, TimeUnit unit, boolean interruptibly) throws InterruptedException {
        // 尝试拿锁, 如果能拿到就直接返回
        long threadId = Thread.currentThread().getId();
        Long ttl = tryAcquire(-1, leaseTime, unit, threadId);
        // lock acquired
        if (ttl == null) {
            return;
        }

        RFuture future = subscribe(threadId);
        if (interruptibly) {
            commandExecutor.syncSubscriptionInterrupted(future);
        } else {
            commandExecutor.syncSubscription(future);
        }

        // 如果拿不到锁就尝试一直轮循, 直到成功获取锁或者异常终止
        try {
            while (true) {
                ttl = tryAcquire(-1, leaseTime, unit, threadId);
                // lock acquired
                if (ttl == null) {
                    break;
                }

                ...

            }
        } finally {
            unsubscribe(future, threadId);
        }
    }

1.1、tryAcquire

    private Long tryAcquire(long waitTime, long leaseTime, TimeUnit unit, long threadId) {
        return get(tryAcquireAsync(waitTime, leaseTime, unit, threadId));
    }

    private  RFuture tryAcquireAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId) {
        RFuture ttlRemainingFuture;
        // 调用真正获取锁的操作
        if (leaseTime != -1) {
            ttlRemainingFuture = tryLockInnerAsync(waitTime, leaseTime, unit, threadId, RedisCommands.EVAL_LONG);
        } else {
            ttlRemainingFuture = tryLockInnerAsync(waitTime, internalLockLeaseTime,
                    TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);
        }
        ttlRemainingFuture.onComplete((ttlRemaining, e) -> {
            if (e != null) {
                return;
            }

            // lock acquired
            // 这里是成功获取了锁, 尝试给锁续约
            if (ttlRemaining == null) {
                if (leaseTime != -1) {
                    internalLockLeaseTime = unit.toMillis(leaseTime);
                } else {
                    scheduleExpirationRenewal(threadId);
                }
            }
        });
        return ttlRemainingFuture;
    }

    // 通过lua脚本真正执行加锁的操作
     RFuture tryLockInnerAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand command) {
        // 如果key不存在, 那正好, 直接set并设置过期时间
        // 如果key存在, 就有两种情况需要考虑
        //   - 同一线程获取重入锁,直接将field(也就是getLockName(threadId))对应的value值+1
        //   - 不同线程竞争锁, 此次加锁失败, 并直接返回此key对应的过期时间
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,
                "if (redis.call('exists', KEYS[1]) == 0) then " +
                        "redis.call('hincrby', KEYS[1], ARGV[2], 1); " +
                        "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                        "return nil; " +
                        "end; " +
                        "if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then " +
                        "redis.call('hincrby', KEYS[1], ARGV[2], 1); " +
                        "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                        "return nil; " +
                        "end; " +
                        "return redis.call('pttl', KEYS[1]);",
                Collections.singletonList(getRawName()), unit.toMillis(leaseTime), getLockName(threadId));
    }

1.2、scheduleExpirationRenewal给锁续约

    protected void scheduleExpirationRenewal(long threadId) {
        ExpirationEntry entry = new ExpirationEntry();
        ExpirationEntry oldEntry = EXPIRATION_RENEWAL_MAP.putIfAbsent(getEntryName(), entry);
        if (oldEntry != null) {
            oldEntry.addThreadId(threadId);
        } else {
            entry.addThreadId(threadId);
            // 续约操作
            renewExpiration();
        }
    }

    private void renewExpiration() {
        ExpirationEntry ee = EXPIRATION_RENEWAL_MAP.get(getEntryName());
        if (ee == null) {
            return;
        }
        
        // 设置延迟任务task, 在时长internalLockLeaseTime/3之后执行, 定期给锁续期
        Timeout task = commandExecutor.getConnectionManager().newTimeout(new TimerTask() {
            @Override
            public void run(Timeout timeout) throws Exception {
                ExpirationEntry ent = EXPIRATION_RENEWAL_MAP.get(getEntryName());
                if (ent == null) {
                    return;
                }
                Long threadId = ent.getFirstThreadId();
                if (threadId == null) {
                    return;
                }
                
                // 真正执行续期命令操作
                RFuture future = renewExpirationAsync(threadId);
                future.onComplete((res, e) -> {
                    if (e != null) {
                        log.error("Can't update lock " + getRawName() + " expiration", e);
                        EXPIRATION_RENEWAL_MAP.remove(getEntryName());
                        return;
                    }
                    
                    // 这次续期之后, 继续schedule自己, 达到持续续期的效果
                    if (res) {
                        // reschedule itself
                        renewExpiration();
                    }
                });
            }
        }, internalLockLeaseTime / 3, TimeUnit.MILLISECONDS);
        
        ee.setTimeout(task);
    }

    // 所谓续期, 就是将expire过期时间再延长
    protected RFuture renewExpirationAsync(long threadId) {
        // 如果key以及当前线程存在, 则延长expire时间, 并返回1代表成功;否则返回0代表失败
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,
                "if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then " +
                        "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                        "return 1; " +
                        "end; " +
                        "return 0;",
                Collections.singletonList(getRawName()),
                internalLockLeaseTime, getLockName(threadId));
    }

2、unlock解锁操作

  public void unlock() {
        try {
            get(unlockAsync(Thread.currentThread().getId()));
        } catch (RedisException e) {
            ...
        }
     
    }

    public RFuture unlockAsync(long threadId) {
        RPromise result = new RedissonPromise<>();
        // 执行解锁操作
        RFuture future = unlockInnerAsync(threadId);

        // 操作成功之后做的事
        future.onComplete((opStatus, e) -> {
            // 取消续约task
            cancelExpirationRenewal(threadId);
            
            ...

        });

        return result;
    }

    protected RFuture unlockInnerAsync(long threadId) {
        // 如果key以及当前线程对应的记录已经不存在, 直接返回空
        // 否在将field(也就是getLockName(threadId))对应的value减1
        //   - 如果减去1之后值还大于0, 那么重新延长过期时间
        //   - 如果减去之后值小于等于0, 那么直接删除key, 并发布订阅消息
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,
                "if (redis.call('hexists', KEYS[1], ARGV[3]) == 0) then " +
                        "return nil;" +
                        "end; " +
                        "local counter = redis.call('hincrby', KEYS[1], ARGV[3], -1); " +
                        "if (counter > 0) then " +
                        "redis.call('pexpire', KEYS[1], ARGV[2]); " +
                        "return 0; " +
                        "else " +
                        "redis.call('del', KEYS[1]); " +
                        "redis.call('publish', KEYS[2], ARGV[1]); " +
                        "return 1; " +
                        "end; " +
                        "return nil;",
                Arrays.asList(getRawName(), getChannelName()), LockPubSub.UNLOCK_MESSAGE, internalLockLeaseTime, getLockName(threadId));
    }

以上便是redisson对redis分布式锁的加/解锁具体实现,主要解决了以下几个问题

    1、死锁问题:设置过期时间

    2、可重入问题:重入+1, 释放锁-1,当值=0时代表完全释放锁

    3、续约问题:可解决锁提前释放问题

    4、锁释放:谁加锁就由谁来释放

总结:

本文由一个线上问题做引子,通过redis分布式锁的常用实现方案,最终选定redisson的解决方案; 并分析redisson的具体实现细节

参考:

Redisson官方文档 - 分布式锁和同步器

Redisson官方文档 - 配置方法

CSDN - 如何使用Redis实现分布式锁?

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