问题
项目采用spring-boot-starter-data-redis，RedisTemplate中没有同时设置NX和EX的方法，如果使用setIfAbsent()方法也就是NX，再设置过期时间expire()也就是EX,如果在设置EX时失败则会造成死锁。在jedis中提供了同时设置NX和EX的方法，这里通过RedisTemplate的execute()方法获取Jedis。
存在问题
解决方案可以可以参考Redisson
- 哨兵模式下有问题，Master挂了可能没有复制到Slave导致锁丢失
- 如果是多个系统redis配置的库不同会有问题
- 因为是不公平锁，所以可能会出现饥饿的情况
- 不支持重入
- 如果执行时间大于锁过期时间，则会破坏原子性
实现
package com.bailian.scloud.util;
import com.bailian.scloud.service.impl.CloudMbBasicInfoServiceImpl;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.dao.DataAccessException;
import org.springframework.data.redis.connection.RedisConnection;
import org.springframework.data.redis.connection.RedisConnectionFactory;
import org.springframework.data.redis.connection.jedis.JedisConnection;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisConnectionUtils;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.core.script.RedisScript;
import org.springframework.stereotype.Component;
import org.springframework.util.ReflectionUtils;
import redis.clients.jedis.Jedis;
import redis.clients.jedis.JedisCluster;
import redis.clients.jedis.JedisCommands;
import java.lang.reflect.Field;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.UUID;
/**
* @program: scloud-support
* @description: Redis锁
* 不完美可以参考
* @see <a href=https://redis.io/topics/distlock)/>
* @see <a href=https://github.com/redisson/redisson/>
* @author: weijiankai
* @create: 2020-01-15 15:25
**/
//TODO 可以参考Redisson
// 1.哨兵模式下有问题，Master挂了可能没有复制到Slave导致锁丢失
// 2.如果是多个系统redis配置的库不同会有问题
// 3.因为是不公平锁，所以可能会出现饥饿的情况
// 4.不支持重入
// 5.如果执行时间大于锁过期时间，则会破坏原子性
public class RedisLockUtil {
private static Logger log = LoggerFactory.getLogger(RedisLockUtil.class);
private static final String LOCK_SUCCESS = "OK";
private static final Long RELEASE_SUCCESS = 1L;
private static final String SET_IF_NOT_EXIST = "NX";
private static final String SET_WITH_EXPIRE_TIME = "PX";
private RedisTemplate redisTemplate;
/**
* 分布式锁的键值
*/
private String lockKey;
/**
* 锁的超时时间 10s
*/
int expireTime = 10 * 1000;
/**
* 锁等待，防止线程饥饿 10s
*/
int acquireTimeout = 20 * 1000;
/**
* 获取指定键值的锁
*
* @param lockKey 锁的键值
*/
public RedisLockUtil(RedisTemplate redisTemplate, String lockKey) {
this.redisTemplate = redisTemplate;
this.lockKey = lockKey;
}
/**
* 获取指定键值的锁,同时设置获取锁超时时间
*
* @param lockKey 锁的键值
* @param acquireTimeout 获取锁超时时间
*/
public RedisLockUtil(RedisTemplate redisTemplate, String lockKey, int acquireTimeout) {
this.redisTemplate = redisTemplate;
this.lockKey = lockKey;
this.acquireTimeout = acquireTimeout;
}
/**
* 获取指定键值的锁,同时设置获取锁超时时间和锁过期时间
*
* @param lockKey 锁的键值
* @param acquireTimeout 获取锁超时时间
* @param expireTime 锁失效时间
*/
public RedisLockUtil(RedisTemplate redisTemplate, String lockKey, int acquireTimeout, int expireTime) {
this.redisTemplate = redisTemplate;
this.lockKey = lockKey;
this.acquireTimeout = acquireTimeout;
this.expireTime = expireTime;
}
public String acquire() {
try {
// 获取锁的超时时间，超过这个时间则放弃获取锁
long end = System.currentTimeMillis() + acquireTimeout;
// 随机生成一个value
SnowflakeIdWorkerUtils idWorker = new SnowflakeIdWorkerUtils(0, 1);
String requireToken = idWorker.nextId();
while (System.currentTimeMillis() < end) {
//获取jedis客户端,原因redisTemplate没有同时是指NX和EX的方法
String result = (String) redisTemplate.execute((RedisCallback<String>) connection -> {
JedisCommands commands = (JedisCommands) connection.getNativeConnection();
return commands.set(lockKey, requireToken, SET_IF_NOT_EXIST, SET_WITH_EXPIRE_TIME, expireTime);
});
if (LOCK_SUCCESS.equals(result)) {
return requireToken;
}
try {
Thread.sleep(100);
} catch (InterruptedException e) {
Thread.currentThread().interrupt();
}
}
} catch (Exception e) {
log.error("acquire lock due to error", e);
}
return null;
}
public boolean release(String identify) {
if (identify == null) {
return false;
}
String script = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";
Object result = new Object();
try {
result = redisTemplate.execute((RedisCallback<Long>) connection -> {
Object nativeConnection = connection.getNativeConnection();
//集群模式
if (nativeConnection instanceof JedisCluster) {
return (Long) ((JedisCluster) nativeConnection).eval(script, Collections.singletonList(lockKey),
Collections.singletonList(identify));
}// 单机模式
else if (nativeConnection instanceof Jedis) {
return (Long) ((Jedis) nativeConnection).eval(script, Collections.singletonList(lockKey),
Collections.singletonList(identify));
}else {
return 0L;
}
});
if (RELEASE_SUCCESS.equals(result)) {
log.info("release lock success, requestToken:{}", identify);
return true;
}
} catch (Exception e) {
log.error("release lock due to error", e);
}
log.info("release lock failed, requestToken:{}, result:{}", identify, result);
return false;
}
}