public class CommonConsumerService {
    //庫存?zhèn)€數(shù)
    static int goodsCount = 900;
    //賣出個數(shù)
    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("剩余庫存：" + goodsCount + " 賣出個數(shù)" + ++saleCount);
                }
            }).start();
        }
        Thread.sleep(3000);
    }
}

運行一次，最后幾行的輸出結(jié)果如下，很明顯出錯了，剩余0個商品卻只賣出了899個商品，很明顯有商品被某個線程私吞了。

...
剩余庫存：5 賣出個數(shù)893
剩余庫存：5 賣出個數(shù)894
剩余庫存：4 賣出個數(shù)895
剩余庫存：2 賣出個數(shù)896
剩余庫存：2 賣出個數(shù)897
剩余庫存：1 賣出個數(shù)898
剩余庫存：0 賣出個數(shù)899

二、使用redis加鎖

redis是單線程的，串行執(zhí)行，那么接下來使用redis為資源進行加鎖。

1.首先引入依賴

compile "org.springframework.boot:spring-boot-starter-data-redis"

2.引入redis加鎖工具類

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;
    /**
     * 嘗試獲取分布式鎖
     * @param jedis      Redis客戶端
     * @param lockKey    鎖
     * @param requestId  請求標識
     * @param expireTime 超期時間
     * @return 是否獲取成功
     */
    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;
    }
    /**
     * 釋放分布式鎖
     * @param jedis     Redis客戶端
     * @param lockKey   鎖
     * @param requestId 請求標識
     * @return 是否釋放成功
     */
    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;
    }
}

3.將上面沒有鎖的示例代碼改編如下：

public class RedisLockConsumerService {
    //庫存?zhèn)€數(shù)
    static int goodsCount = 900;
    //賣出個數(shù)
    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("剩余庫存：" + goodsCount + " 賣出個數(shù)" + ++saleCount);
                    }
                }
                RedisTool.releaseDistributedLock(jedis, "goodsCount", Thread.currentThread().getName());
                jedis.close();
            }).start();
        }
        Thread.sleep(3000);
        jedisPool.close();
    }
}

執(zhí)行幾次程序輸出結(jié)果如下，可以看到結(jié)果是有序，并且正確的。