Redis-Redis 高并发分布式锁

集群分布式场景高并发

1.negix配置代理和路由

高并发场景超卖问题

1.使用原生redis控制超卖时(若是商品，则可以将商品id作为锁对象)，会遇到的问题

问题一：若直接使用：将获取锁的对象和设置的超时的时间分开，则不能控制原子性，如下所示

         Boolean result = stringRedisTemplate.opsForValue().setIfAbsent(lockKey, "zhuge");
        stringRedisTemplate.expire(lockKey, 10, TimeUnit.SECONDS);

 问题二：若直接使用：将获取锁的对象和设置的超时的时间放在一个原子操作里执行时，在临界条件下，当程序执行到最后准备释放锁时候，锁的超时时间已到，则此时的锁成为已过期，则释放不了锁；而当下一个线程也来执行任务时，前一个任务将这个任务所拿的所给释放掉了（释放掉不属于自己的锁对象）；则引入redisson分布式锁来解决当前的问题，redisson具有锁续命机制

@RestController
public class IndexController {

    @Autowired
    private Redisson redisson;
    @Autowired
    private StringRedisTemplate stringRedisTemplate;
    @Autowired
    private RedisTemplate redisTemplate;

    @RequestMapping("/deduct_stock")
    public String deductStock() {
        String lockKey = "lock:product_101";
        //Boolean result = stringRedisTemplate.opsForValue().setIfAbsent(lockKey, "zhuge");
        //stringRedisTemplate.expire(lockKey, 10, TimeUnit.SECONDS);
       String clientId = UUID.randomUUID().toString();
        Boolean result = stringRedisTemplate.opsForValue().setIfAbsent(lockKey, clientId, 30, TimeUnit.SECONDS); //jedis.setnx(k,v)
        if (!result) {
            return "error_code";
        }
  
        try {
            int stock = Integer.parseInt(stringRedisTemplate.opsForValue().get("stock")); // jedis.get("stock")
            if (stock > 0) {
                int realStock = stock - 1;
                stringRedisTemplate.opsForValue().set("stock", realStock + ""); // jedis.set(key,value)
                System.out.println("扣减成功，剩余库存:" + realStock);
            } else {
                System.out.println("扣减失败，库存不足");
            }
        } finally {
           if (clientId.equals(stringRedisTemplate.opsForValue().get(lockKey))) {
                stringRedisTemplate.delete(lockKey);
            }
        }


        return "end";
    }

使用分布式锁redisson

redisson使用

引入对应的redission的jar包

        
			org.redisson
			redisson
			3.6.5
		

 设置redission配置

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @Bean
    public Redisson redisson() {
        // 此为单机模式
        Config config = new Config();
        config.useSingleServer().setAddress("redis://localhost:6379").setDatabase(0);
        return (Redisson) Redisson.create(config);
    }

}

 redission的基本使用

@RestController
public class IndexController {

    @Autowired
    private Redisson redisson;
    @Autowired
    private StringRedisTemplate stringRedisTemplate;
    @Autowired
    private RedisTemplate redisTemplate;

    @RequestMapping("/deduct_stock")
    public String deductStock() {
        String lockKey = "lock:product_101";
        //Boolean result = stringRedisTemplate.opsForValue().setIfAbsent(lockKey, "zhuge");
        //stringRedisTemplate.expire(lockKey, 10, TimeUnit.SECONDS);
        /*String clientId = UUID.randomUUID().toString();
        Boolean result = stringRedisTemplate.opsForValue().setIfAbsent(lockKey, clientId, 30, TimeUnit.SECONDS); //jedis.setnx(k,v)
        if (!result) {
            return "error_code";
        }*/
        //获取锁对象
        RLock redissonLock = redisson.getLock(lockKey);
        //加分布式锁
        redissonLock.lock();  //  .setIfAbsent(lockKey, clientId, 30, TimeUnit.SECONDS);
        try {
            int stock = Integer.parseInt(stringRedisTemplate.opsForValue().get("stock")); // jedis.get("stock")
            if (stock > 0) {
                int realStock = stock - 1;
                stringRedisTemplate.opsForValue().set("stock", realStock + ""); // jedis.set(key,value)
                System.out.println("扣减成功，剩余库存:" + realStock);
            } else {
                System.out.println("扣减失败，库存不足");
            }
        } finally {
            /*if (clientId.equals(stringRedisTemplate.opsForValue().get(lockKey))) {
                stringRedisTemplate.delete(lockKey);
            }*/
            //解锁
            redissonLock.unlock();
        }


        return "end";
    }

Redission执行的逻辑流程

 Redission分布式锁加锁源码分析

        redissonLock.lock(); 

加锁 

 @Override
    public void lockInterruptibly() throws InterruptedException {
        lockInterruptibly(-1, null);
    }

执行 lockInterruptibly加锁逻辑

@Override
    public void lockInterruptibly(long leaseTime, TimeUnit unit) throws InterruptedException {
        long threadId = Thread.currentThread().getId();
        Long ttl = tryAcquire(leaseTime, unit, threadId); //尝试去加锁，返回的时加锁后的过期时间
        // lock acquired
        if (ttl == null) {  //若ttl为null ,则表示加锁成功 ;若ttl不为null ,则往下走
            return;
        }

        RFuture future = subscribe(threadId); //发布订阅，订阅前者执行的任务若提前执行完，则唤醒机制，去重新获取锁
        commandExecutor.syncSubscription(future);

        try {
            while (true) { //进入循环
                ttl = tryAcquire(leaseTime, unit, threadId); //再次尝试获取锁，返回加锁成功后的过期时间
                // lock acquired
                if (ttl == null) {  //若ttl为null ,则表示加锁成功 ;若ttl不为null ,则往下走
                    break;
                }

                // waiting for message
                if (ttl >= 0) { 若ttl大于o
                    getEntry(threadId).getLatch().tryAcquire(ttl, TimeUnit.MILLISECONDS);
//进行间歇性锁自旋逻辑，不占用cpu资源
                } else {
                    getEntry(threadId).getLatch().acquire();
                }
            }
        } finally {
            unsubscribe(future, threadId);
        }
//        get(lockAsync(leaseTime, unit));
    }

执行tryAcquire(leaseTime, unit, threadId)尝试加锁逻辑

 private  RFuture tryAcquireAsync(long leaseTime, TimeUnit unit, final long threadId) {
        if (leaseTime != -1) {
            return tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_LONG);
        }
//leaseTime 默认设置为-1
        RFuture ttlRemainingFuture = tryLockInnerAsync(commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout(), TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);
//执行加锁逻辑
        ttlRemainingFuture.addListener(new FutureListener() { //异步执行，锁续命逻辑
            @Override
            public void operationComplete(Future future) throws Exception {
                if (!future.isSuccess()) { //若加锁不成功，则退出
                    return;
                }

                Long ttlRemaining = future.getNow(); //若加锁成功，则ttlRemaining 为null
                // lock acquired
                if (ttlRemaining == null) {
                    scheduleExpirationRenewal(threadId); //加锁成功，则执行锁续命逻辑
                }
            }
        });
        return ttlRemainingFuture;
    }

执行tryLockInnerAsync(commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout(), TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG); 加锁逻辑

   RFuture tryLockInnerAsync(long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand command) {
//通过lua脚本来执行加锁逻辑，来保证原子性
        internalLockLeaseTime = unit.toMillis(leaseTime);

        return commandExecutor.evalWriteAsync(getName(), LongCodec.INSTANCE, command,
            //执行加锁逻辑 （key,argv与下面所传参数一一对应）
                  "if (redis.call('exists', KEYS[1]) == 0) then " +      
            //KEY[1]表示下面的getName(),
                      "redis.call('hset', KEYS[1], ARGV[2], 1); " +    
            //ARGV[2]表示下面的getLockName(threadId)
                      "redis.call('pexpire', KEYS[1], ARGV[1]); " + 
            //ARGV[1]表示下面的internalLockLeaseTime
                      "return nil; " +
                  "end; " +
//执行锁重入逻辑（一个线程对同一个锁对象进行多次加锁，此为重入锁逻辑）
                  "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]);", //设置返回过期时间
                    Collections.