SpringBoot中如何使用Redis作为全局锁
一、模拟没有锁情况下的资源竞争
public class CommonConsumerService { //库存个数 static int goodsCount = 900; //卖出个数 static int saleCount = 0; public static void main(String[] args) throws InterruptedException { for (int i = 0; i < 1000; i++) { new Thread(() -> { try {Thread.sleep(2);} catch (InterruptedException e) {} if (goodsCount > 0) { goodsCount--; System.out.println("剩余库存:" + goodsCount + " 卖出个数" + ++saleCount); } }).start(); } Thread.sleep(3000); } }登录后复制
运行一次,最后几行的输出结果如下,很明显出错了,剩余0个商品却只卖出了899个商品,很明显有商品被某个线程私吞了。
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剩余库存:5 卖出个数893
剩余库存:5 卖出个数894
剩余库存:4 卖出个数895
剩余库存:2 卖出个数896
剩余库存:2 卖出个数897
剩余库存:1 卖出个数898
剩余库存:0 卖出个数899
二、使用redis加锁
redis是单线程的,串行执行,那么接下来使用redis为资源进行加锁。
1.首先引入依赖
compile "org.springframework.boot:spring-boot-starter-data-redis"登录后复制
2.引入redis加锁工具类
package com.kingboy.common.utils; import redis.clients.jedis.Jedis; import java.util.Collections; /** * @author kingboy--KingBoyWorld@163.com * @date 2017/12/29 下午1:57 * @desc Redis工具. */ public class RedisTool { private static final String LOCK_SUCCESS = "OK"; private static final String SET_IF_NOT_EXIST = "NX"; private static final String SET_WITH_EXPIRE_TIME = "PX"; private static final Long RELEASE_SUCCESS = 1L; /** * 尝试获取分布式锁 * @param jedis Redis客户端 * @param lockKey 锁 * @param requestId 请求标识 * @param expireTime 超期时间 * @return 是否获取成功 */ public static boolean tryGetDistributedLock(Jedis jedis, String lockKey, String requestId, int expireTime) { String result = jedis.set(lockKey, requestId, SET_IF_NOT_EXIST, SET_WITH_EXPIRE_TIME, expireTime); if (LOCK_SUCCESS.equals(result)) { return true; } return false; } /** * 释放分布式锁 * @param jedis Redis客户端 * @param lockKey 锁 * @param requestId 请求标识 * @return 是否释放成功 */ public static boolean releaseDistributedLock(Jedis jedis, String lockKey, String requestId) { String script = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end"; Object result = jedis.eval(script, Collections.singletonList(lockKey), Collections.singletonList(requestId)); if (RELEASE_SUCCESS.equals(result)) { return true; } return false; } }登录后复制
3.将上面没有锁的示例代码改编如下:
public class RedisLockConsumerService { //库存个数 static int goodsCount = 900; //卖出个数 static int saleCount = 0; @SneakyThrows public static void main(String[] args) { JedisPool jedisPool = new JedisPool(new JedisPoolConfig(), "192.168.0.130", 6379, 1000); for (int i = 0; i < 1000; i++) { new Thread(() -> { try {Thread.sleep(2);} catch (InterruptedException e) {} Jedis jedis = jedisPool.getResource(); boolean lock = false; while (!lock) { lock = RedisTool.tryGetDistributedLock(jedis, "goodsCount", Thread.currentThread().getName(), 10); } if (lock) { if (goodsCount > 0) { goodsCount--; System.out.println("剩余库存:" + goodsCount + " 卖出个数" + ++saleCount); } } RedisTool.releaseDistributedLock(jedis, "goodsCount", Thread.currentThread().getName()); jedis.close(); }).start(); } Thread.sleep(3000); jedisPool.close(); } }登录后复制
执行几次程序输出结果如下,可以看到结果是有序,并且正确的。
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剩余库存:6 卖出个数894
剩余库存:5 卖出个数895
剩余库存:4 卖出个数896
剩余库存:3 卖出个数897
剩余库存:2 卖出个数898
剩余库存:1 卖出个数899
剩余库存:0 卖出个数900