近期工作遇到需要业务场景如下,需要每天定时推送给另一系统一批数据,但是由于系统是集群部署的,会造成统一情况下任务争用的情况,所以需要增加分布式锁来保证一定时间范围内有一个Job来完成定时任务. 前期考虑的方案有采用ZooKeeper分布式任务,Quartz分布式任务调度,但是由于Zookeeper需要增加额外组件,Quartz需要增加表,并且项目中现在已经有Redis这一组件存在,所以考虑采用Redis分布式锁的情况来完成分布式任务抢占这一功能

记录一下走过的弯路.

第一版本:

	@Override 	public <T> Long set(String key,T value, Long cacheSeconds) { 		if (value instanceof HashMap) { 			BoundHashOperations valueOperations = redisTemplate.boundHashOps(key); 			valueOperations.putAll((Map) value); 			valueOperations.expire(cacheSeconds, TimeUnit.SECONDS); 		} 		else{ 		//使用map存储 		BoundHashOperations valueOperations = redisTemplate.boundHashOps(key); 		valueOperations.put(key, value); 		//秒 		valueOperations.expire(cacheSeconds, TimeUnit.SECONDS); 		} 		return null; 	}   	@Override 	public void del(String key) { 		redisTemplate.delete(key); 	} 

采用set 和 del 完成锁的占用与释放,后经测试得知,set不是线程安全,在并发情况下常常会导致数据不一致.

第二版本:

    /**      * 分布式锁      * @param range 锁的长度 允许有多少个请求抢占资源      * @param key      * @return      */     public boolean getLock(int range, String key) {         ValueOperations<String, Integer> valueOper1 = template.opsForValue();         return valueOper1.increment(key, 1) <= range;     }      /**      * 初始化锁, 设置等于0      * @param key      * @param expireSeconds      * @return      */     public void initLock(String key, Long expireSeconds) {         ValueOperations<String, Integer> operations = template.opsForValue();         template.setKeySerializer(new GenericJackson2JsonRedisSerializer());         template.setValueSerializer(new GenericJackson2JsonRedisSerializer());         operations.set(key, 0, expireSeconds * 1000);     }      /**      * 释放锁      * @param key      */     public void releaseLock(String key) {         ValueOperations<String, Integer> operations = template.opsForValue();         template.setKeySerializer(new GenericJackson2JsonRedisSerializer());         template.setValueSerializer(new GenericJackson2JsonRedisSerializer());         template.delete(key);     } 

采用redis的 increament操作完成锁的抢占.但是释放锁时,是每个线程都可以删除redis中的key值.

最终版本:

import org.springframework.beans.factory.annotation.Autowired; import org.springframework.data.redis.connection.RedisConnectionFactory; import org.springframework.data.redis.connection.jedis.JedisConnection; import org.springframework.stereotype.Service; import org.springframework.util.ReflectionUtils; import redis.clients.jedis.Jedis;  import java.lang.reflect.Field; import java.util.Collections;  @Service public class RedisLock {      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;      @Autowired     private RedisConnectionFactory connectionFactory;      /**      * 尝试获取分布式锁      * @param lockKey 锁      * @param requestId 请求标识      * @param expireTime 超期时间      * @return 是否获取成功      */     public boolean lock(String lockKey, String requestId, int expireTime) {         Field jedisField = ReflectionUtils.findField(JedisConnection.class, "jedis");         ReflectionUtils.makeAccessible(jedisField);         Jedis jedis = (Jedis) ReflectionUtils.getField(jedisField, connectionFactory.getConnection());          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 lockKey 锁      * @param requestId 请求标识      * @return 是否释放成功      */     public boolean releaseLock(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 = getJedis().eval(script, Collections.singletonList(lockKey), Collections.singletonList(requestId));          if (RELEASE_SUCCESS.equals(result)) {             return true;         }         return false;      }      public Jedis getJedis() {         Field jedisField = ReflectionUtils.findField(JedisConnection.class, "jedis");         ReflectionUtils.makeAccessible(jedisField);         Jedis jedis = (Jedis) ReflectionUtils.getField(jedisField, connectionFactory.getConnection());         return jedis;     }  } 

最终释放锁用的是lua脚本,能够做到原子性操作.

例子在 https://gitee.com/InvitusTeam/Spring-boot-Demo