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com.soento.redis.lang.RedisDistributedLock Maven / Gradle / Ivy
package com.soento.redis.lang;
import com.soento.core.lang.DistributedLock;
import lombok.extern.slf4j.Slf4j;
import org.springframework.data.redis.core.RedisCallback;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.serializer.StringRedisSerializer;
/**
* Redis分布式锁
*
* @author soento
*/
@Slf4j
public class RedisDistributedLock extends DistributedLock {
private RedisTemplate redisTemplate;
private static final int DEFAULT_ACQUIRE_RESOLUTION_MILLIS = 100;
private static final int EXPIRE_MSECS = 60 * 1000;
private static final int TIMEOUT_MSECS = 10 * 1000;
/**
* 锁超时时间，防止线程在入锁以后，无限的执行等待
*/
private int expireMsecs;
/**
* 锁等待时间，防止线程饥饿
*/
private int timeoutMsecs;
public RedisDistributedLock(RedisTemplate redisTemplate, String lockKey) {
this(redisTemplate, lockKey, TIMEOUT_MSECS, EXPIRE_MSECS);
}
public RedisDistributedLock(RedisTemplate redisTemplate, String lockKey, int timeoutMsecs) {
this(redisTemplate, lockKey, timeoutMsecs, EXPIRE_MSECS);
}
public RedisDistributedLock(RedisTemplate redisTemplate, String lockKey, int timeoutMsecs, int expireMsecs) {
this.redisTemplate = redisTemplate;
this.lockKey = LOCK_PREFIX + lockKey;
this.timeoutMsecs = timeoutMsecs;
this.expireMsecs = expireMsecs;
log.info("初始化Redis锁，lockKey：{}", this.lockKey);
log.info("初始化Redis锁，锁超时时间：{}", this.expireMsecs);
log.info("初始化Redis锁，锁等待时间：{}", this.timeoutMsecs);
}
private String get(final String key) {
Object obj = null;
try {
obj = redisTemplate.execute((RedisCallback) connection -> {
StringRedisSerializer serializer = new StringRedisSerializer();
byte[] data = connection.get(serializer.serialize(key));
connection.close();
if (data == null) {
return null;
}
return serializer.deserialize(data);
});
} catch (Exception e) {
log.error("get redis error, key : " + key, e);
}
return obj != null ? obj.toString() : null;
}
private boolean setNX(final String key, final String value) {
Object obj = null;
try {
obj = redisTemplate.execute((RedisCallback) connection -> {
StringRedisSerializer serializer = new StringRedisSerializer();
Boolean success = connection.setNX(serializer.serialize(key), serializer.serialize(value));
connection.close();
return success;
});
} catch (Exception e) {
log.error("setNX redis error, key : " + key, e);
}
return obj != null ? (Boolean) obj : false;
}
private String getSet(final String key, final String value) {
Object obj = null;
try {
obj = redisTemplate.execute((RedisCallback) connection -> {
StringRedisSerializer serializer = new StringRedisSerializer();
byte[] ret = connection.getSet(serializer.serialize(key), serializer.serialize(value));
connection.close();
return serializer.deserialize(ret);
});
} catch (Exception e) {
log.error("setNX redis error, key : " + key, e);
}
return obj != null ? (String) obj : null;
}
/**
* 获得 lock.
* 实现思路: 主要是使用了redis 的setnx命令,缓存了锁.
* reids缓存的key是锁的key,所有的共享, value是锁的到期时间(注意:这里把过期时间放在value了,没有时间上设置其超时时间)
* 执行过程:
* 1.通过setnx尝试设置某个key的值,成功(当前没有这个锁)则返回,成功获得锁
* 2.锁已经存在则获取锁的到期时间,和当前时间比较,超时的话,则设置新的值
*
* @return true：成功获取, false：获取锁超时
*/
@Override
public synchronized boolean acquire() {
try {
int timeout = timeoutMsecs;
while (timeout >= 0) {
long expires = System.currentTimeMillis() + expireMsecs + 1;
//锁到期时间
String expiresStr = String.valueOf(expires);
if (this.setNX(lockKey, expiresStr)) {
// lock acquired
locked = true;
log.info("锁定成功，lockKey：{}，锁超时时间：{}", this.lockKey, expiresStr);
return true;
}
//redis里的时间
String currentValueStr = this.get(lockKey);
if (currentValueStr != null && Long.parseLong(currentValueStr) < System.currentTimeMillis()) {
//判断是否为空，不为空的情况下，如果被其他线程设置了值，则第二个条件判断是过不去的
// lock is expired
String oldValueStr = this.getSet(lockKey, expiresStr);
//获取上一个锁到期时间，并设置现在的锁到期时间，
//只有一个线程才能获取上一个线上的设置时间，因为jedis.getSet是同步的
if (oldValueStr != null && oldValueStr.equals(currentValueStr)) {
//防止误删（覆盖，因为key是相同的）了他人的锁——这里达不到效果，这里值会被覆盖，但是因为什么相差了很少的时间，所以可以接受
//[分布式的情况下]:如过这个时候，多个线程恰好都到了这里，但是只有一个线程的设置值和当前值相同，他才有权利获取锁
// lock acquired
locked = true;
log.info("锁定成功，lockKey：{}，锁超时时间：{}", this.lockKey, expiresStr);
return true;
}
}
log.info("尝试获取锁定，lockKey：{}，等待时间时间：{}", this.lockKey, DEFAULT_ACQUIRE_RESOLUTION_MILLIS);
timeout -= DEFAULT_ACQUIRE_RESOLUTION_MILLIS;
/*
延迟100 毫秒, 这里使用随机时间可能会好一点,可以防止饥饿进程的出现,即,当同时到达多个进程,
只会有一个进程获得锁,其他的都用同样的频率进行尝试,后面有来了一些进行,也以同样的频率申请锁,这将可能导致前面来的锁得不到满足.
使用随机的等待时间可以一定程度上保证公平性
*/
Thread.sleep(DEFAULT_ACQUIRE_RESOLUTION_MILLIS);
}
return false;
} catch (Throwable e) {
log.error(e.getMessage(), e);
return false;
}
}
/**
* Acqurired lock release.
*/
@Override
public synchronized void release() {
try {
if (locked) {
if (!redisTemplate.delete(lockKey)) {
log.error("delete redis key error, key : {}", lockKey);
} else {
log.info("释放锁成功，lockKey：{}", this.lockKey);
}
locked = false;
}
} catch (Throwable e) {
log.error(e.getMessage(), e);
}
}
}
