package com.common.redis.util;
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import org.slf4j.Logger;
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import org.slf4j.LoggerFactory;
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import org.springframework.dao.DataAccessException;
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import org.springframework.data.redis.connection.RedisConnection;
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import org.springframework.data.redis.core.RedisCallback;
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import org.springframework.data.redis.core.RedisTemplate;
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import org.springframework.data.redis.serializer.StringRedisSerializer;
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import java.util.Objects;
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public class RedisLockUtil {
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private final static Logger log = LoggerFactory.getLogger(RedisLockUtil.class);
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private RedisTemplate<String, Object> redisTemplate;
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public RedisLockUtil(RedisTemplate<String, Object> template) {
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this.redisTemplate = template;
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}
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private static final int DEFAULT_ACQUIRY_RESOLUTION_MILLIS = 100;
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/**
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* 锁超时时间，防止线程在入锁以后，无限的执行等待
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*/
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private int expireMsecs = 60 * 1000;
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/**
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* 锁等待时间，防止线程饥饿
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*/
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private int timeoutMsecs = 10 * 1000;
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private volatile boolean locked = false;
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private String get(final String key) {
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Object obj = null;
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try {
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obj = redisTemplate.execute(new RedisCallback<Object>() {
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@Override
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public Object doInRedis(RedisConnection connection) throws DataAccessException {
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StringRedisSerializer serializer = new StringRedisSerializer();
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byte[] data = connection.get(serializer.serialize(key));
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connection.close();
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if (data == null) {
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return null;
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}
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return serializer.deserialize(data);
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}
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});
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} catch (Exception e) {
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log.error("get redis error, key : {}", key);
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}
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return obj != null ? obj.toString() : null;
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}
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private boolean setNX(final String key, final String value) {
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Object obj = null;
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try {
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obj = redisTemplate.execute(new RedisCallback<Object>() {
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@Override
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public Object doInRedis(RedisConnection connection) throws DataAccessException {
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StringRedisSerializer serializer = new StringRedisSerializer();
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Boolean success = connection.setNX(serializer.serialize(key), serializer.serialize(value));
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connection.close();
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return success;
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}
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});
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} catch (Exception e) {
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log.error("setNX redis error, key : {}", key);
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}
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return obj != null ? (Boolean) obj : false;
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}
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private String getSet(final String key, final String value) {
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Object obj = null;
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try {
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obj = redisTemplate.execute(new RedisCallback<Object>() {
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@Override
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public Object doInRedis(RedisConnection connection) throws DataAccessException {
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StringRedisSerializer serializer = new StringRedisSerializer();
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byte[] ret = connection.getSet(serializer.serialize(key), serializer.serialize(value));
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connection.close();
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return serializer.deserialize(ret);
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}
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});
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} catch (Exception e) {
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log.error("setNX redis error, key : {}", key);
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}
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return obj != null ? (String) obj : null;
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}
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/**
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* 获得 lock.
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* 实现思路: 主要是使用了redis 的setnx命令,缓存了锁.
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* 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)
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* 执行过程:
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* 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
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* 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
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*
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* @return true if lock is acquired, false acquire timeouted
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* @throws InterruptedException in case of thread interruption
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*/
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public synchronized boolean lock(String lockKey) throws InterruptedException {
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int timeout = timeoutMsecs;
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while (timeout >= 0) {
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long expires = System.currentTimeMillis() + expireMsecs + 1;
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String expiresStr = String.valueOf(expires); //锁到期时间
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if (this.setNX(lockKey, expiresStr)) {
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// lock acquired
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locked = true;
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return true;
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}
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String currentValueStr = this.get(lockKey); //redis里的时间
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if (currentValueStr != null && Long.parseLong(currentValueStr) < System.currentTimeMillis()) {
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//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
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// lock is expired
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String oldValueStr = this.getSet(lockKey, expiresStr);
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//获取上一个锁到期时间，并设置现在的锁到期时间，
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//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
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if (oldValueStr != null && oldValueStr.equals(currentValueStr)) {
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//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
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//[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
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// lock acquired
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locked = true;
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return true;
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}
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}
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timeout -= DEFAULT_ACQUIRY_RESOLUTION_MILLIS;
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/*
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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,
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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.
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使用随机的等待时间可以一定程度上保证公平性
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*/
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Thread.sleep(DEFAULT_ACQUIRY_RESOLUTION_MILLIS);
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}
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return false;
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}
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/**
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* Acqurired lock release.
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*/
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public synchronized void unlock(String lockKey) {
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if (locked) {
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redisTemplate.delete(lockKey);
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locked = false;
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}
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}
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public boolean lock(String lockKey, long lockExpireMils) {
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return (Boolean) redisTemplate.execute((RedisCallback) connection -> {
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long nowTime = System.currentTimeMillis();
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Boolean acquire = connection.set(lockKey.getBytes(), String.valueOf(nowTime + lockExpireMils + 1).getBytes());
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if (acquire) {
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return Boolean.TRUE;
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} else {
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byte[] value = connection.get(lockKey.getBytes());
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if (Objects.nonNull(value) && value.length > 0) {
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long oldTime = Long.parseLong(new String(value));
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if (oldTime < nowTime) {
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//connection.getSet：返回这个key的旧值并设置新值。
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byte[] oldValue = connection.getSet(lockKey.getBytes(), String.valueOf(nowTime + lockExpireMils + 1).getBytes());
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//当key不存时会返回空，表示key不存在或者已在管道中使用
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return oldValue == null ? false : Long.parseLong(new String(oldValue)) < nowTime;
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}
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}
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}
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return Boolean.FALSE;
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});
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}
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}
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