Redis seckill demo

Scheme 1 : Method plus synchronized that will do , Thread safety scheme , But the efficiency of execution is low , Not suitable for large concurrent occasions

Option two ： Use optimistic lock  

controller:

@RestController
public class SecondKill {

    @Autowired
    SecondKillSev secondKillSev;

    @RequestMapping(value = "/buy",method = RequestMethod.POST)
    public Mes buy(@RequestParam("proid") String proid){
        String usedId=new Random().nextInt(1000)+"";
        Mes mes = secondKillSev.doSecondKill(usedId, proid);
        return mes;
    }
}

service:

@Service
public class SecondKillSev {

    Mes message;

    public SecondKillSev(){

    }

    @Autowired
    StringRedisTemplate stringRedisTemplate;

    /**
     *  Execute seckill 
     *  Scheme 1 ：synchronized, Thread safety , But the efficiency of execution is low , Not suitable for large concurrent occasions 
     *  Option two ： Monitor transactions with optimistic locks 
     */
    public Mes doSecondKill(String uid, String proid){

        //1. Judge uid and proid Non empty 
        if(uid==null || proid==null){
            return Mes.getMes("400","uid and proid Can't be empty ");
        }

        //2. Connect redis
        ValueOperations<String, String> ops = stringRedisTemplate.opsForValue();

        //3. Splicing key, stock key, Successful user key
        String kcKey="kcKey:"+proid;
        String userKey="userKey:"+proid;

        // Optimistic lock solves oversold problem 
        //stringRedisTemplate The default is not to open things 
        stringRedisTemplate.setEnableTransactionSupport(true);

        List<Object> txResults = stringRedisTemplate.execute(new SessionCallback<List<Object>>() {
            public List<Object> execute(RedisOperations operations) throws DataAccessException {
                // Monitor inventory 
                operations.watch(kcKey);
                //4. Get inventory , If the inventory is null, The second kill has not yet started 
                String kc=ops.get(kcKey);
                if(kc==null){
                    message= Mes.getMes("400"," The stock is null, The second kill hasn't started yet ");
                    return null;
                }

                //5. Judge whether the user repeats the second kill 
                if(operations.opsForSet().isMember(userKey, uid)){
                    message=Mes.getMes("400"," You can't repeat the second kill ");
                    return null;
                }

                //6. Judge the quantity of goods , If the quantity is less than 1, Then the second kill is over 
                if(Integer.parseInt(kc)<=0){
                    message=Mes.getMes("400"," The second kill is over ");
                    return null;
                }

                //7. Second kill process , stock -1, Successful user added to manifest 
                // With a transaction 
                operations.multi();
                operations.opsForValue().decrement(kcKey);
                operations.opsForSet().add(userKey,uid);

                List exec = operations.exec();
                if(exec==null || exec.size()==0){
                    message=Mes.getMes("400"," Seckill failure ");
                    return null;
                }else{
                    return exec;
                }
            }
        });

        if(txResults==null ||txResults.size()==0){
            return message;
        }

        return Mes.getMes("200"," Seckill success ");
    }
}

But this scheme also has a disadvantage , That is, if the quantity of goods is 500, But the number of threads is 1000, That is, when the number of visits is not very large , There will be the problem that the inventory is not sold out , That is, inventory leftover problems , So it can be used lua Script to solve ;

Option three :lua Script

local userid=KEYS[1];
local prodid=KEYS[2];
local qtkey="sk:"..prodid..":qt";
local userskey="sk:"..prodid..":user";
local userExists=redis.call("sismember",userskey,userid);
if tonumber(userExists)==1 then
  return 2;
end
local num=redis.call("get",qtkey);
if tonumber(num)<=0 then
  return 0;
else
  redis.call("decr",qtkey);
  redis.call("sadd",userskey,userid);
  end
  return 1

Code implementation :

@Service
public class SeckillByScript {
    static String secKillScript1 = "local userid=KEYS[1];\n" +
            "local prodid=KEYS[2];\n" +
            "local qtkey=\"sk:\"..prodid..\":qt\";\n" +
            "local userskey=\"sk:\"..prodid..\":user\";\n" +
            "local userExists=redis.call(\"sismember\",userskey,userid);" +
            "if tonumber(userExists)==1 then\n" +
            "  return 2;\n" +
            "end\n" +
            "local num=redis.call(\"get\",qtkey);\n" +
            "if tonumber(num)<=0 then\n" +
            "  return 0;\n" +
            "else\n" +
            "  redis.call(\"decr\",qtkey);\n" +
            "  redis.call(\"sadd\",userskey,userid);\n" +
            "  end\n" +
            "  return 1";

    public boolean doSecKill(String userid, String prodid) {
        JedisPool jedisPool = JedisPoolUtil.getJedisPool();
        Jedis jedis = jedisPool.getResource();
        String sha1 = jedis.scriptLoad(secKillScript1);
        Object result = jedis.evalsha(sha1, 2, userid, prodid);
        String reString = String.valueOf(result);
        if ("0".equals(reString)) {
            System.out.println(" Empty ！");
            return false;
        } else if ("1".equals(reString)) {
            System.out.println(" Panic buying ");
            return true;
        } else if ("2".equals(reString)) {
            System.out.println(" The user has robbed ！");
            return false;
        } else {
            System.out.println(" Panic buying exception ");
            return false;
        }
    }
}