点评项目---分布式锁

什么是分布式锁

分布式锁:满足分布式系统或集群模式下多进程可见并且互斥的锁。

分布式锁的实现

基于Redis的分布式锁

初级版本

java 复制代码

package com.hmdp.utils;

import org.springframework.data.redis.core.StringRedisTemplate;

import java.util.concurrent.TimeUnit;


public class SimpleRedisLock implements ILock{

    private String name;
    private StringRedisTemplate stringRedisTemplate;

    public SimpleRedisLock(String name, StringRedisTemplate stringRedisTemplate) {
        this.name = name;
        this.stringRedisTemplate = stringRedisTemplate;
    }

    private final static String KEY_PREFIX = "lock:";

    @Override
    public boolean tryLock(long timeoutSec) {
        // 获取线程id
        long threadId = Thread.currentThread().getId();
        // 获取锁
        Boolean success = stringRedisTemplate.opsForValue().setIfAbsent(KEY_PREFIX + name, threadId + "", timeoutSec, TimeUnit.SECONDS);

        return Boolean.TRUE.equals(success);
    }

    @Override
    public void unLock() {
        //释放锁
        stringRedisTemplate.delete(KEY_PREFIX + name);

    }
}

java 复制代码

 package com.hmdp.service.impl;

import com.hmdp.dto.Result;
import com.hmdp.entity.SeckillVoucher;
import com.hmdp.entity.User;
import com.hmdp.entity.VoucherOrder;
import com.hmdp.mapper.VoucherOrderMapper;
import com.hmdp.service.ISeckillVoucherService;
import com.hmdp.service.IVoucherOrderService;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.hmdp.utils.RedisIdWorker;
import com.hmdp.utils.SimpleRedisLock;
import com.hmdp.utils.UserHolder;
import org.springframework.aop.framework.AopContext;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import java.time.LocalDateTime;

/**
 * <p>
 *  服务实现类
 * </p>
 *
 * @author 虎哥
 * @since 2021-12-22
 */
@Service
public class VoucherOrderServiceImpl extends ServiceImpl<VoucherOrderMapper, VoucherOrder> implements IVoucherOrderService {

    @Autowired
    private RedisIdWorker redisIdWorker;
    @Autowired
    private ISeckillVoucherService seckillVoucherService;
    @Autowired
    private StringRedisTemplate stringRedisTemplate;


    @Override
    public Result seckillVoucher(Long voucherId) {
        //1.查询优惠券
        SeckillVoucher voucher = seckillVoucherService.getById(voucherId);

        //2.判断秒杀是否开始
        if(voucher.getBeginTime().isAfter(LocalDateTime.now())){
            return Result.fail("秒杀尚未开始");
        }
        //3.判断秒杀是否结束
        if(voucher.getEndTime().isBefore(LocalDateTime.now())){
            return Result.fail("秒杀已结束");
        }

        //4.判断库存是否充足
        if(voucher.getStock() < 1){
            return Result.fail("库存不足");
        }

        //5.实现分布式锁 解决多个线程对同一资源进行操作
        Long userId = UserHolder.getUser().getId();
        SimpleRedisLock lock = new SimpleRedisLock("order"+userId,stringRedisTemplate);
        boolean isLock = lock.tryLock(1200);
        if(!isLock){
            return Result.fail("请勿重复下单");
        }
        //悲观锁
//        synchronized (userId.toString().intern()){
        //获取代理对象（事务）
        try {
            IVoucherOrderService proxy = (IVoucherOrderService) AopContext.currentProxy();
            return proxy.createVoucherOrder(voucherId);
        }finally {
            lock.unLock();
        }
//        }
    }

    @Transactional
    public Result createVoucherOrder(Long voucherId) {
        //一人一单
        Long userId = UserHolder.getUser().getId();
        int count = query().eq("user_id", userId)
                .eq("voucher_id", voucherId)
                .eq("user_id",userId)
                .count();
        //判断是否存在
        if(count > 0){
            //用户已经购买过
            return Result.fail("用户已经购买过一次");
        }
        //5.扣减库存
        boolean success = seckillVoucherService.update()
                .setSql("stock = stock - 1")
                .eq("voucher_id", voucherId)
                // 库存必须大于0 乐观锁改动
                .gt("stock",0)
                .update();
        if(!success){
            return Result.fail("库存不足");
        }
        //6.创建订单
        VoucherOrder voucherOrder = new VoucherOrder();
        //7.返回订单id
        Long orderId = redisIdWorker.nextId("order");
        voucherOrder.setId(orderId);
        //8.设置用户id
        voucherOrder.setUserId(userId);
        //9.设置优惠券id
        voucherOrder.setVoucherId(voucherId);
        save(voucherOrder);

        //返回订单id
        return Result.ok(orderId);
    }
}

解决Redis分布式锁误删问题

java 复制代码

package com.hmdp.utils;

import cn.hutool.core.lang.UUID;
import org.springframework.data.redis.core.StringRedisTemplate;

import java.util.concurrent.TimeUnit;


public class SimpleRedisLock implements ILock{

    private String name;
    private StringRedisTemplate stringRedisTemplate;

    public SimpleRedisLock(String name, StringRedisTemplate stringRedisTemplate) {
        this.name = name;
        this.stringRedisTemplate = stringRedisTemplate;
    }

    private final static String KEY_PREFIX = "lock:";

    private final static String ID_PREFIX =UUID.randomUUID().toString(true) + "-";

    @Override
    public boolean tryLock(long timeoutSec) {
        // 获取线程标示
        String threadId = ID_PREFIX + Thread.currentThread().getId();
        // 获取锁
        Boolean success = stringRedisTemplate.opsForValue().setIfAbsent(KEY_PREFIX + name, threadId, timeoutSec, TimeUnit.SECONDS);

        return Boolean.TRUE.equals(success);
    }

    @Override
    public void unLock() {
        // 获取线程标示
        String threadId = ID_PREFIX + Thread.currentThread().getId();
        //获取锁中的标示
        String id = stringRedisTemplate.opsForValue().get(KEY_PREFIX + name);

        //判断标示是否一致
        if(threadId.equals(id)){
            //释放锁
            stringRedisTemplate.delete(KEY_PREFIX + name);
        }
    }
}

分布式锁的原子性问题

Lua脚本解决多条命令原子性问题

Redis提供了Lua脚本功能，在一个脚本中编写多条Redis命令，确保多条命令执行时的原子性。Lua是一种编程语言,它的基本语法大家可以参考网站:https://www.runoob.com/lua/lua-tutorial.html

java调用Lua脚本改造分布式锁

java 复制代码

package com.hmdp.utils;

import cn.hutool.core.lang.UUID;
import org.springframework.core.io.ClassPathResource;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.data.redis.core.script.DefaultRedisScript;
import org.springframework.data.redis.core.script.RedisScript;

import java.util.Collections;
import java.util.concurrent.TimeUnit;


public class SimpleRedisLock implements ILock{

    private String name;
    private StringRedisTemplate stringRedisTemplate;

    public SimpleRedisLock(String name, StringRedisTemplate stringRedisTemplate) {
        this.name = name;
        this.stringRedisTemplate = stringRedisTemplate;
    }

    private final static String KEY_PREFIX = "lock:";
    private final static String ID_PREFIX =UUID.randomUUID().toString(true) + "-";
    private final static DefaultRedisScript<Long> UNLOCK_SCRIPT;
    static {
        UNLOCK_SCRIPT = new DefaultRedisScript<>();
        UNLOCK_SCRIPT.setLocation(new ClassPathResource("unlock.lua"));
        UNLOCK_SCRIPT.setResultType(Long.class);
    }

    @Override
    public boolean tryLock(long timeoutSec) {
        // 获取线程标示
        String threadId = ID_PREFIX + Thread.currentThread().getId();
        // 获取锁
        Boolean success = stringRedisTemplate.opsForValue().setIfAbsent(KEY_PREFIX + name, threadId, timeoutSec, TimeUnit.SECONDS);

        return Boolean.TRUE.equals(success);
    }

    @Override
    public void unLock() {
        //调用lua脚本
        stringRedisTemplate.execute(
                UNLOCK_SCRIPT,
                Collections.singletonList(KEY_PREFIX + name),
                ID_PREFIX + Thread.currentThread().getId()
                );


    }

//    // 获取线程标示
//    String threadId = ID_PREFIX + Thread.currentThread().getId();
//    //获取锁中的标示
//    String id = stringRedisTemplate.opsForValue().get(KEY_PREFIX + name);
//
//    //判断标示是否一致
//        if(threadId.equals(id)){
//        //释放锁
//        stringRedisTemplate.delete(KEY_PREFIX + name);
//    }
}

lua 复制代码

--lua脚本
--比较线程标示是否与锁标示一致
if(redis.call('get', KEYS[1]) == ARGV[1]) then
  --释放锁 del key
  return redis.call('del', KEYS[1])
else
  return 0
end