淺析Redis分布式鎖

更新時(shí)間：2017年12月21日 10:28:45 投稿：laozhang

本篇文章通過(guò)實(shí)例給大家講解了Redis分布式鎖工作原理以及用法分享，有需要的朋友參考學(xué)習(xí)下吧。

近期工作遇到需要業(yè)務(wù)場(chǎng)景如下,需要每天定時(shí)推送給另一系統(tǒng)一批數(shù)據(jù),但是由于系統(tǒng)是集群部署的,會(huì)造成統(tǒng)一情況下任務(wù)爭(zhēng)用的情況,所以需要增加分布式鎖來(lái)保證一定時(shí)間范圍內(nèi)有一個(gè)Job來(lái)完成定時(shí)任務(wù). 前期考慮的方案有采用ZooKeeper分布式任務(wù),Quartz分布式任務(wù)調(diào)度,但是由于Zookeeper需要增加額外組件,Quartz需要增加表,并且項(xiàng)目中現(xiàn)在已經(jīng)有Redis這一組件存在,所以考慮采用Redis分布式鎖的情況來(lái)完成分布式任務(wù)搶占這一功能

記錄一下走過(guò)的彎路.

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存儲(chǔ)
		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 完成鎖的占用與釋放,后經(jīng)測(cè)試得知,set不是線程安全,在并發(fā)情況下常常會(huì)導(dǎo)致數(shù)據(jù)不一致.

第二版本:

/**
   * 分布式鎖
   * @param range 鎖的長(zhǎng)度 允許有多少個(gè)請(qǐng)求搶占資源
   * @param key
   * @return
   */
  public boolean getLock(int range, String key) {
    ValueOperations<String, Integer> valueOper1 = template.opsForValue();
    return valueOper1.increment(key, 1) <= range;
  }

  /**
   * 初始化鎖, 設(shè)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);
  }

  /**
   * 釋放鎖
   * @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操作完成鎖的搶占.但是釋放鎖時(shí),是每個(gè)線程都可以刪除redis中的key值. 并且initLock會(huì)降上一次的操作給覆蓋掉，所以也廢棄掉此方法

最終版本:

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;
  /**
   * 嘗試獲取分布式鎖
   * @param lockKey 鎖
   * @param requestId 請(qǐng)求標(biāo)識(shí)
   * @param expireTime 超期時(shí)間
   * @return 是否獲取成功
   */
  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;

  }
  /**
   * 釋放分布式鎖
   * @param lockKey 鎖
   * @param requestId 請(qǐng)求標(biāo)識(shí)
   * @return 是否釋放成功
   */
  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;
  }
}