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<>一、使用场景
通常在分布式系统中，我们经常会从数据库中读取数据和修改数据，然而这不是一个原子操作，在并发时就会导致数据的不正确，例如一会下面的电商秒杀，库存数量的更新就会遇到。
<>二、实现锁的条件
1.互斥性：在任何时候，都有一个客户端持有锁
2.不能出现死锁：即在一个客户端持有锁的期间内，如果客户端出现故障也不能影响后续的客户端可以持有锁
3.保证上锁和解锁的是同一个客户端
<>三、具体实现
*
<>setnx+expire (加锁)
setnx k1 value1 expire 5 seconds #成功返回1，在键k1不存在的时候将key的值设置为value1 setnx k1
value2 expire 5 seconds #失败返回0，因为k1已经存在值value1了，相当于已经有客户端吃锁了，设置失败 del k1
#删除k1的值，成功返回1，这里的del相当于释放锁 setnx k1 value2 expire 5 seconds #成功，返回1 type
orderService struct { orderRepository repository.OrderRepository goodsService
service.IGoodsService redis *redis.Client } func (s *orderService)
tryLock(userId, goodsId, lockId int64) (err error) { var res bool //Redis
Setnx命令在指定的 key 不存在时，为 key 设置指定的值（key存在了不能覆盖） if res, err =
s.redis.SetNX(service.Ctx, fmt.Sprintf("lock:%d:%d", userId, goodsId), lockId,
time.Minute).Result(); err != nil { log.Printf("redis.SetNx() failed, err: %v",
err) err = code.RedisErr return } if !res { err = code.MiaoshaFailed } return }
*
<>lua脚本
if redis.call('setnx',KEYS[1],ARGV[1]) == 1 then
redis.call('expire',KEYS[1],ARGV[2]) else return 0 end;
*
<>设置ttl
SET key value [EX seconds] [PX milliseconds] [NX|XX]
EX seconds：将键的过期时间设置为seconds秒。
PX milliseconds：将键的过期时间设置为milliseconds毫秒。
NX ： 只在键不存在时， 才对键进行设置操作。
XX ： 只在键已经存在时， 才对键进行设置操作。
