在分布锁的实际使用中，可能会遇到一种情况，一个业务执行时间很长，已经超过redis加锁的时间，也就是锁已经释放了，但是业务还没执行完成，这时候其它线程还是可以获取锁，那就没保证线程安全

项目环境：

• JDK 1.8

• SpringBoot 2.2.1

• Maven 3.2+

• Mysql 8.0.26

• spring-boot-starter-data-redis 2.2.1

• jedis3.1.0

• 开发工具

  • IntelliJ IDEA

  • smartGit

先搭建一个springboot集成jedis的例子工程，参考我之前的博客，

抽象类，实现一些共用的逻辑

package com.example.jedis.common;import lombok.extern.slf4j.Slf4j;import java.net.SocketTimeoutException;
import java.util.concurrent.TimeUnit;import static com.example.jedis.common.RedisConstant.DEFAULT_EXPIRE;
import static com.example.jedis.common.RedisConstant.DEFAULT_TIMEOUT;@Slf4j
public abstract class AbstractDistributedLock implements DistributedLock {@Overridepublic boolean acquire(String lockKey, String requestId, int expireTime, int timeout) {expireTime = expireTime <= 0 ? DEFAULT_EXPIRE : expireTime;timeout = timeout < 0 ? DEFAULT_TIMEOUT : timeout * 1000;long start = System.currentTimeMillis();try {do {if (doAcquire(lockKey, requestId, expireTime)) {watchDog(lockKey, requestId, expireTime);return true;}TimeUnit.MILLISECONDS.sleep(100);} while (System.currentTimeMillis() - start < timeout);} catch (Exception e) {Throwable cause = e.getCause();if (cause instanceof SocketTimeoutException) {// ignore exceptionlog.error("sockTimeout exception:{}", e);}else if (cause instanceof  InterruptedException) {// ignore exceptionlog.error("Interrupted exception:{}", e);}else {log.error("lock acquire exception:{}", e);}throw new LockException(e.getMessage(), e);}return false;}@Overridepublic boolean release(String lockKey, String requestId) {try {return doRelease(lockKey, requestId);} catch (Exception e) {log.error("lock release exception:{}", e);throw new LockException(e.getMessage(), e);}}protected abstract boolean doAcquire(String lockKey, String requestId, int expireTime);protected abstract boolean doRelease(String lockKey, String requestId);protected abstract void watchDog(String lockKey, String requestId, int expireTime);}

具体的实现，主要是基于一个定时任务，时间间隔一定要比加锁时间少一点，这里暂时少1s，加上一个lua脚本进行检测，检测不到数据，就关了定时任务

package com.example.jedis.common;import cn.hutool.core.collection.CollUtil;
import cn.hutool.core.convert.Convert;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.InitializingBean;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;import java.util.List;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;@Component
@Slf4j
public class JedisLockTemplate extends AbstractRedisLock implements InitializingBean {private String UNLOCK_LUA = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";private String WATCH_DOG_LUA = "local lock_key=KEYS[1]\n" +"local lock_value=ARGV[1]\n" +"local lock_ttl=ARGV[2]\n" +"local current_value=redis.call('get',lock_key)\n" +"local result=0\n" +"if lock_value==current_value then\n" +"    redis.call('expire',lock_key,lock_ttl)\n" +"    result=1\n" +"end\n" +"return result";private static final Long UNLOCK_SUCCESS = 1L;private static final Long RENEWAL_SUCCESS = 1L;@Autowiredprivate JedisTemplate jedisTemplate;private ScheduledThreadPoolExecutor scheduledExecutorService;@Overridepublic void afterPropertiesSet() throws Exception {this.UNLOCK_LUA = jedisTemplate.scriptLoad(UNLOCK_LUA);this.WATCH_DOG_LUA = jedisTemplate.scriptLoad(WATCH_DOG_LUA);scheduledExecutorService = new ScheduledThreadPoolExecutor(1);}@Overridepublic boolean doAcquire(String lockKey, String requestId, int expire) {return jedisTemplate.setnxex(lockKey, requestId, expire);}@Overridepublic boolean doRelease(String lockKey, String requestId) {Object eval = jedisTemplate.evalsha(UNLOCK_LUA, CollUtil.newArrayList(lockKey), CollUtil.newArrayList(requestId));if (UNLOCK_SUCCESS.equals(eval)) {scheduledExecutorService.shutdown();return true;}return false;}@Overridepublic void watchDog(String lockKey, String requestId, int expire) {int period = getPeriod(expire);if (scheduledExecutorService.isShutdown()) {scheduledExecutorService = new ScheduledThreadPoolExecutor(1);}scheduledExecutorService.scheduleAtFixedRate(new WatchDogTask(scheduledExecutorService, CollUtil.newArrayList(lockKey), CollUtil.newArrayList(requestId, Convert.toStr(expire))),1,period,TimeUnit.SECONDS);}class WatchDogTask implements Runnable {private ScheduledThreadPoolExecutor scheduledThreadPoolExecutor;private List<String> keys;private List<String> args;public WatchDogTask(ScheduledThreadPoolExecutor scheduledThreadPoolExecutor, List<String> keys, List<String> args) {this.scheduledThreadPoolExecutor = scheduledThreadPoolExecutor;this.keys = keys;this.args = args;}@Overridepublic void run() {log.info("watch dog for renewal...");Object evalsha = jedisTemplate.evalsha(WATCH_DOG_LUA, keys, args);if (!evalsha.equals(RENEWAL_SUCCESS)) {scheduledThreadPoolExecutor.shutdown();}log.info("renewal result:{}, keys:{}, args:{}", evalsha, keys, args);}}private int getPeriod(int expire) {if (expire < 1)throw new LockException("expire不允许小于1");return expire - 1;}}

写一个测试Controller类，开始用SpringBoot测试类的，但是发现有时候还是经常出现一些连接超时情况，这个可能是框架兼容的bug

package com.example.jedis.controller;import com.example.jedis.common.JedisLockTemplate;
import com.example.jedis.common.Lock;
import lombok.extern.slf4j.Slf4j;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;import java.util.Random;
import java.util.concurrent.CountDownLatch;
import java.util.stream.IntStream;@RestController
@Slf4j
public class TestController {private static final String REDIS_KEY = "test:lock";@Autowiredprivate JedisLockTemplate jedisLockTemplate;@GetMapping("test")public void test(@RequestParam("threadNum")Integer threadNum) throws InterruptedException {CountDownLatch countDownLatch = new CountDownLatch(threadNum);IntStream.range(0, threadNum).forEach(e->{new Thread(new RunnableTask(countDownLatch)).start();});countDownLatch.await();}@GetMapping("testLock")@Lock(lockKey = "test:api", requestId = "123", expire = 5, timeout = 3)public void testLock() throws InterruptedException {doSomeThing();}class RunnableTask implements Runnable {CountDownLatch countDownLatch;public RunnableTask(CountDownLatch countDownLatch) {this.countDownLatch = countDownLatch;}@Overridepublic void run() {redisLock();countDownLatch.countDown();}}private void redisLock() {String requestId = getRequestId();Boolean lock = jedisLockTemplate.acquire(REDIS_KEY, requestId, 5, 3);if (lock) {try {doSomeThing();} catch (Exception e) {jedisLockTemplate.release(REDIS_KEY, requestId);} finally {jedisLockTemplate.release(REDIS_KEY, requestId);}} else {log.warn("获取锁失败!");}}private void doSomeThing() throws InterruptedException {log.info("do some thing");Thread.sleep(15 * 1000);}private String getRequestId() {String str="abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";Random random=new Random();StringBuffer sb=new StringBuffer();for(int i=0;i<32;i++){int number=random.nextInt(62);sb.append(str.charAt(number));}return sb.toString();}}

# 模拟100个并发请求
curl http://127.0.0.1:8080/springboot-jedis/test?threadNum=100

长事务还没执行完成，会自动进行续期

模拟100个线程的场景，只有一个线程会获取到锁

参考资料：

• https://github.com/finefuture/RedisLock-with-WatchDog/blob/master/RedisLock.java
  
• https://www.cnblogs.com/crazymakercircle/p/14731826.html
• https://blog.csdn.net/Cocoxzq000/article/details/121575272