redis分布式锁

作者: eblly | 来源:发表于2019-07-28 22:49 被阅读0次

场景 & 原理

分布式场景中，经常需要保证在多个jvm进程中，在同一时刻只有一个线程对某一条数据进行操作。
例如：资金问题，甲用户同时支付了两笔订单，第一笔订单请求进入了A节点，第二笔订单请求进入了B节点。
在这个情况下，我们通常不允许同一时刻有个线程对资金进行操作，毕竟这太危险了。因此需要分布式锁，锁住其他线程的操作（类似单JVM下的synchronized）。

分布式锁可见性如下图：

image.png

分布式原理如下图：

image.png

代码

上代码。。。


import lombok.Getter;
import lombok.Setter;
import lombok.ToString;
import lombok.extern.log4j.Log4j2;

import java.util.concurrent.CountDownLatch;

/**
 * 甲用户发起多笔支付订单，分布式保证不并发扣款。
 *
 * @author eblly
 * @since 2019/7/28
 */
@Log4j2
public class RedisLockTest {
    static String redisKey = "balance:jia";

    public static void main(String[] args) throws InterruptedException {
        String host = "127.0.0.1";
        int    port = 6379;

        RedisClient redisUtil = RedisClient.builder()
                                           .setHost(host)
                                           .setPort(port)
                                           .build();

        int            size           = 10;
        CountDownLatch countDownLatch = new CountDownLatch(size);
        Balance        balance        = new Balance();
        balance.setUserName("甲用户");
        balance.setBalance(100);

        for (int i = 1; i <= size; i++) {
            String          hodler   = "running" + i;
            BalanceRunnable runnable = new BalanceRunnable(balance, redisUtil, hodler, i, countDownLatch);
            Thread          thread   = new Thread(runnable);

            thread.start();
        }

        countDownLatch.await();
        log.info("最后剩余金额, balance: {}", balance);
    }

    /**
     *
     */
    static class BalanceRunnable implements Runnable {
        private String         holder;
        private RedisClient    redisUtil;
        private Balance        balance;
        private int            fee;
        private CountDownLatch countDownLatch;

        public BalanceRunnable(Balance balance, RedisClient redisUtil, String threadName, int fee,
                               CountDownLatch countDownLatch) {
            this.balance = balance;
            this.redisUtil = redisUtil;
            this.holder = threadName;
            this.fee = fee;
            this.countDownLatch = countDownLatch;
        }

        @Override
        public void run() {
            while (true) {
                String value = redisUtil.get(redisKey);

                boolean isPay = false;
                if (value != null) {
                    log.info("用户资金被锁住");
                } else {
                    if (!isPay && lock(redisKey, holder)) {

                        // 扣款成功
                        balance.setBalance(balance.getBalance() - fee);

                        log.info("剩余balance: {} , fee: {}", balance.getBalance(), fee);
                        isPay = true;
                    }
                }

                // 已扣款, 尝试释放锁
                if (isPay && unlock(redisKey, holder)) {
                    countDownLatch.countDown();
                    // 释放锁并退出
                    break;
                }

                // 等待锁
                try {
                    Thread.sleep(50L);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }

        /**
         * 锁资源
         *
         * @param key
         * @param value
         * @return
         */
        public boolean lock(String key, String value) {
            String valueRedis = redisUtil.get(key);

            // 判断是否获取 可重入锁
            if (valueRedis != null) {
                if (value.equals(valueRedis)) {
                    return true;
                } else {
                    return false;
                }
            }

            if (redisUtil.setnx(key, value) > 0) {
                return true;
            }

            return false;
        }


        /**
         * 释放锁
         *
         * @param key
         * @param value
         * @return
         */
        public boolean unlock(String key, String value) {
            String valueRedis = redisUtil.get(key);

            if (valueRedis == null) {
                return true;
            }

            // 值不相等，不是锁的持有者
            if (!valueRedis.equals(value)) {
                return false;
            }

            redisUtil.del(key);
            return true;
        }
    }
}


@Setter
@Getter
@ToString
class Balance {
    private String userName;

    private Integer balance;
}

运行结果:

==> 剩余balance: 97 , fee: 3
==> 剩余balance: 90 , fee: 7
==> 用户资金被锁住
==> 剩余balance: 80 , fee: 10
==> 剩余balance: 79 , fee: 1
==> 剩余balance: 70 , fee: 9
==> 剩余balance: 64 , fee: 6
==> 剩余balance: 56 , fee: 8
==> 剩余balance: 54 , fee: 2
==> 剩余balance: 49 , fee: 5
==> 用户资金被锁住
==> 剩余balance: 45 , fee: 4
==> 最后剩余金额, balance: Balance(userName=甲用户, balance=45)

版本2

RedisUtil源码 https://gist.github.com/eblly/2b11f05d027ecb678d6d410bf7138daa

上面的版本存在锁超时没有释放，会导致其他节点的操作一直阻塞。
因此，需要改进：

加时间超时
使用lua作为原子操作

import lombok.extern.log4j.Log4j2;

import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;
import java.util.concurrent.CountDownLatch;

/**
 * 甲用户发起多笔支付订单，分布式保证不并发扣款。
 *
 * @author eblly
 * @since 2019/7/28
 */
@Log4j2
public class RedisLockTest_v2 {
    private static String         redisKey = "balance:jia";
    private static Queue<Integer> feeQueue = new ConcurrentLinkedQueue<>();

    public static void main(String[] args) throws InterruptedException {
        String host = "127.0.0.1";
        int    port = 6379;

        RedisClient redisClient = RedisClient.builder()
                                             .setHost(host)
                                             .setPort(port)
                                             .build();

        int            size           = 100;
        int            balanceSize    = 100000;
        CountDownLatch countDownLatch = new CountDownLatch(size);
        Balance        balance        = new Balance();
        balance.setUserName("甲用户");
        balance.setBalance(balanceSize);

        // TODO 加入cycri barr , 保证所有线程一起开始
        for (int i = 1; i <= size; i++) {
            String          hodler   = "running" + i;
            BalanceRunnable runnable = new BalanceRunnable(balance, redisClient, hodler, i, countDownLatch);
            Thread          thread   = new Thread(runnable);

            thread.start();
        }

        countDownLatch.await();

//        log.info("sizeQueue: {}", feeQueue);
        int feeTotal = 0;

        for (Integer fee : feeQueue) {
            feeTotal += fee;
        }

        int residue = balanceSize - feeTotal;
        log.info("==========> 线程数: {}", size);
        log.info("最后剩余金额, balance: {} , residue: {}", balance, residue);

        if (balance.getBalance() == residue) {
            log.info("===========> 正常");
        } else {
            log.error("===========> 不正常");
        }
    }

    /**
     *
     */
    static class BalanceRunnable implements Runnable {
        private String         holder;
        private RedisClient    redisClient;
        private Balance        balance;
        private int            fee;
        private CountDownLatch countDownLatch;

        public BalanceRunnable(Balance balance, RedisClient redisClient, String threadName, int fee,
                               CountDownLatch countDownLatch) {
            this.balance = balance;
            this.redisClient = redisClient;
            this.holder = threadName;
            this.fee = fee;
            this.countDownLatch = countDownLatch;
        }

        @Override
        public void run() {
            while (true) {
                String value = redisClient.getLock(redisKey);

                if (value != null && !holder.equals(value)) {
                    log.info("用户资金被锁住, 锁: {}", value);
                } else {
                    if (redisClient.lock(redisKey, holder)) {

                        // 扣款成功
                        balance.setBalance(balance.getBalance() - fee);

                        feeQueue.add(fee);
                        log.info("剩余balance: {} , fee: {}", balance.getBalance(), fee);

                        // 已扣款, 尝试释放锁
                        if (redisClient.unlock(redisKey, holder)) {
                            countDownLatch.countDown();
                            // 释放锁并退出
                            log.info("释放锁并退出");
                            break;
                        }
                    }
                }
                // 等待锁释放
                try {
                    Thread.sleep(50L);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

锁操作代码

 /**
     * 获取锁
     * @param key
     * @param <T>
     * @return
     */
    public <T> T getLock(Object key) {
        Jedis jedis = getJedis();
        try {
            return (T) jedis.get(String.valueOf(key));
        } finally {close(jedis);}
    }

    /**
     * 锁资源
     *
     * @param key
     * @param value
     * @return
     */
    public boolean lock(String key, String value) {
        String expire = "30";

        String script = " if redis.call('get',KEYS[1]) then " +
                " return redis.call('get',KEYS[1]) " +
                " else " +
                " return redis.call('setex',KEYS[1],ARGV[2],ARGV[1]) " +
                " end";
        Object eval = eval(script, Arrays.asList(key), Arrays.asList(value, expire));
        log.debug("eval: {}", eval);

        if ("OK".equals(eval)) {
            log.debug("===========> OK");
            return true;
        }

        return false;
    }

    /**
     * 释放锁
     *
     * @param key
     * @param value
     * @return
     */
    public boolean unlock(String key, String value) {
        String script = " if redis.call('get',KEYS[1]) == ARGV[1] then return redis.call('del',KEYS[1]) else " +
                " return 0 end ";

        String eval = String.valueOf(eval(script, Arrays.asList(key), Arrays.asList(value)));
        log.debug("eval: {}", eval);

        if ("1".equals(eval)) {
            log.debug("成功释放锁");
            return true;
        }

        return false;
    }

RedisUtil代码在 https://www.jianshu.com/p/6605f9f34ed0

redis分布式锁

场景 & 原理

代码

版本2

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