浅析Redis分布式锁

Redis  /  管理员 发布于 7年前   224

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:

@Overridepublic <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;}@Overridepublic 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. 并且initLock会降上一次的操作给覆盖掉，所以也废弃掉此方法

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;@Servicepublic 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;  }}