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（以下所有内容全部来自上述课程）
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分布式锁

1. Redisson功能介绍

基于setnx实现的分布式锁存在下面的问题：

不可重入：同一个线程无法多次获取同一把锁
不可重试：获取锁只尝试一次就返回false，没有重试机制
超时释放：锁超时释放虽然可以避免死锁，但如果是业务执行耗时较长，也会导致锁释放，存在安全隐患
主从一致性：如果Redis提供了主从集群，主从同步存在延迟，当主宕机时，如果从并同步主中的锁数据，则会出现锁实现

Redisson是一个在Redis的基础上实现的lava驻内存数据网格(In-Memory Data Grid)。它不仅提供了一系列的分布式的Java常用对象，还提供了许多分布式服务，其中就包含了各种分布式锁的实现。
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官网地址:https://redisson.org
GitHub地址:https://github.com/redisson/redisson
jar包下载：https://mvnrepository.com/artifact/org.redisson/redisson/3.50.0

2. Redis入门

引入依赖:

<dependency>
<groupId>org.redisson</groupId><artifactId>redisson</artifactId>
<version>3.13.6</version>
</dependency>

配置Redisson客户端:

@Configuration
public class RedisConfig {@Beanpublic RedissonClient redissonClient(){// 配置类Config config =new Config();//添加redis地址，这里添加了单点的地址，也可以使用config.useClusterServers()添加集群地址	config.useSingleServer().setAddress("redis://192.168.150.101:6379").setPassword("123321");// 创建客户端return Redisson.create(config);}
}

使用Redisson的分布式锁

@Resource
private RedissonClient redissonClient;
@Test
void testRedisson()throws InterruptedException {// 获取锁(可重入)，指定锁的名称RLock lock=redissonClient.getLock("anyLock");//尝试获取锁，参数分别是:获取锁的最大等待时间(期间会重试)，锁自动释放时间，时间单位boolean isLock =lock.tryLock(1，10,TimeUnit.SECONDS);// 判断释放获取成功if(isLock){try {System.out.println("执行业务");}finally {// 释放锁lock.unlock();}}
}

3. Redisson的可重入锁原理

// 创建锁对象
RLock lock=redissonClient.getLock("lock");@Test
void method1(){boolean isLock = lock.tryLock();if(!isLock){log.error("获取锁失败,1");return;}try{log.info("获取锁成功,1");method2();} finally {log.info("释放锁,1");lock.unlock();}
}
void method2(){boolean isLock =lock.tryLock();if(!isLock){log.error("获取锁失败,2");return;}try {log.info("获取锁成功,2");} finally {log.info("释放锁,2");lock.unlock();}
}

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获取锁的lua脚本：

local key = KEYS[1]; -- 锁的key
local threadId= ARGV[1];-- 线程唯一标识
local releaseTime =ARGV[2];-- 锁的自动释放时间
--判断是否存在
if(redis.call('exists',key)== 0)then-- 不存在，获取锁redis.call('hset',key, threadId,"1');-- 设置有效期redis.call('expire',key, releaseTime);return 1;--返回结果
end ;
--锁已经存在，判断threadId是否是自己
if(redis.call("hexists",key,threadId)== 1) then--不存在，获取锁，重入次数+1redis.call("hincrby", key, threadId, '1');--设置有效期redis.call('expire',key, releaseTime);return 1;--返回结果
end ;
return 0; --代码走到这里，说明获取锁的不是自己，获取锁失败

释放锁的lua脚本：

local key =KEYS[1];-- 锁的key
local threadId= ARGV[1];-- 线程唯一标识
local releseTime=ARGV[2];--锁的自动释放时间
--判断当前锁是否还是被自己持有
if(redis.call("HEXISTs",key,threadId)==0)thenreturn nil;--如果已经不是自己，则直接返回
end ;
--是自己的锁，则重入次数-1
local count = redis.call('HINCRBY', key, threadId, -1);
--判断是否重入次数是否已经为0
if(count>0)then--大于0说明不能释放锁，重置有效期然后返回redis.call('EXPIRE',key, releaseTime);return nil;
else--等于0说明可以释放锁，直接删除redis.call('DEL', key);return nil;
end ;

4. Redisson的锁重试和WatchDog机制

tryLock ctrl+alt+B 打开源码

   private Long tryAcquire(long waitTime, long leaseTime, TimeUnit unit, long threadId) { //第三处查看//阻塞等待Future结果，就是剩余有效期 把Long接着返回-->第二处查看（往下滑）return get(tryAcquireAsync0(waitTime, leaseTime, unit, threadId));  //查看tryAcquireAsync0（往下滑）}private RFuture<Long> tryAcquireAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId) {  //第四处查看RFuture<Long> ttlRemainingFuture;if (leaseTime > 0) {ttlRemainingFuture = tryLockInnerAsync(waitTime, leaseTime, unit, threadId, RedisCommands.EVAL_LONG);} else {  //命令行已经发出去了，但是结果拿没拿到还不清楚-->FuturettlRemainingFuture = tryLockInnerAsync(waitTime, internalLockLeaseTime,  //查看tryLockInnerAsync（向下滑）TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);}  //返回第三处查看（向上滑）CompletionStage<Long> s = handleNoSync(threadId, ttlRemainingFuture);ttlRemainingFuture = new CompletableFutureWrapper<>(s);CompletionStage<Long> f = ttlRemainingFuture.thenApply(ttlRemaining -> {// lock acquiredif (ttlRemaining == null) {  //剩余有效期=nullif (leaseTime > 0) {  internalLockLeaseTime = unit.toMillis(leaseTime);} else {scheduleExpirationRenewal(threadId);  //自动更新有效期续约 --> 查看scheduleExpirationRenewal（下一个板块的代码）}}return ttlRemaining;});return new CompletableFutureWrapper<>(f);}@Overridepublic boolean tryLock() {return get(tryLockAsync());}<T> RFuture<T> tryLockInnerAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) { //第五处查看 return evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,"if ((redis.call('exists', KEYS[1]) == 0) " +"or (redis.call('hexists', KEYS[1], ARGV[2]) == 1)) then " +"redis.call('hincrby', KEYS[1], ARGV[2], 1); " +"redis.call('pexpire', KEYS[1], ARGV[1]); " +"return nil; " +"end; " + //上面是获取成功，下面是没成功"return redis.call('pttl', KEYS[1]);",  //pttl（毫秒的单位）=ttl(秒的单位) 获取指定key的剩余有效期Collections.singletonList(getRawName()), unit.toMillis(leaseTime), getLockName(threadId));}  //返回第四处（向上滑）@Overridepublic boolean tryLock(long waitTime, long leaseTime, TimeUnit unit) throws InterruptedException { //第二处查看long time = unit.toMillis(waitTime);    //把等待时间转换为毫秒long current = System.currentTimeMillis();  //获取当前时间long threadId = Thread.currentThread().getId();  //获取当前线程id 也就是线程标识Long ttl = tryAcquire(waitTime, leaseTime, unit, threadId);  //尝试获取锁 -->看tryAcquire方法（往上滑）// lock acquiredif (ttl == null) {return true;  //获取成功。直接返回}//获取失败，继续尝试（重点！）time -= System.currentTimeMillis() - current;  //现在的时间减去之前的当前时间（就是获取锁消耗的时间）//然后最大等待时间减去消耗的时间，就是剩余等待时间if (time <= 0) {acquireFailed(waitTime, unit, threadId);return false;  //没有剩余等待时间，就直接获取失败}//获取失败，继续尝试（但没有立即-->subscribe）current = System.currentTimeMillis();CompletableFuture<RedissonLockEntry> subscribeFuture = subscribe(threadId);  //订阅了别人释放锁的信号（publish）try {subscribeFuture.get(time, TimeUnit.MILLISECONDS);  //因为时间不确定，所以也是Future} catch (TimeoutException e) {if (!subscribeFuture.completeExceptionally(new RedisTimeoutException(  //最大剩余时间结束-->返回false，继续往下走"Unable to acquire subscription lock after " + time + "ms. " +"Try to increase 'subscriptionsPerConnection' and/or 'subscriptionConnectionPoolSize' parameters."))) {subscribeFuture.whenComplete((res, ex) -> {if (ex == null) {  //判断有没有时间了unsubscribe(res, threadId);  //超时，取消订阅}});}acquireFailed(waitTime, unit, threadId);return false;  } catch (ExecutionException e) {acquireFailed(waitTime, unit, threadId);return false;  //获取锁失败}try {time -= System.currentTimeMillis() - current;  //又计算一次等待消耗时间if (time <= 0) {acquireFailed(waitTime, unit, threadId);return false;  //套娃，没时间了还是没获取到锁，直接返回获取失败}//小总结：上方一直计算剩余时间，有就直接到这儿，没有就一直重复计算//计算终于有剩余时间（true）while (true) {long currentTime = System.currentTimeMillis();ttl = tryAcquire(waitTime, leaseTime, unit, threadId);  //第一次重试（tryAcquire）// lock acquiredif (ttl == null) {return true;  //成功}//失败就再计算剩余时间time -= System.currentTimeMillis() - currentTime;if (time <= 0) {acquireFailed(waitTime, unit, threadId);return false;  //没有就失败}// waiting for message  失败就继续计算时间currentTime = System.currentTimeMillis();if (ttl >= 0 && ttl < time) {  //ttl和time ，哪个小就先等哪个（time是根本底线，没了也不用等了）//getLatch()  信号量，类似与publish抛出获取信号//ttl是施放时间，更灵活一些，锁释放了就重试（重新获取锁）commandExecutor.getNow(subscribeFuture).getLatch().tryAcquire(ttl, TimeUnit.MILLISECONDS);} else {  //time到期了，还没释放也就不用等了commandExecutor.getNow(subscribeFuture).getLatch().tryAcquire(time, TimeUnit.MILLISECONDS);}//再获取时间time -= System.currentTimeMillis() - currentTime;if (time <= 0) {  //没时间了，还是直接失败acquireFailed(waitTime, unit, threadId);return false;}}  //时间充足就while(true)，返回上面又开始重试} finally {unsubscribe(commandExecutor.getNow(subscribeFuture), threadId);}
//        return get(tryLockAsync(waitTime, leaseTime, unit));}  //至此，重试问题解决  -->  去看超时问题：第四处（向上滑）

  protected void scheduleExpirationRenewal(long threadId) {ExpirationEntry entry = new ExpirationEntry();//EntryName：当前锁的名称//一个锁一个entry，第一次来创建新的entry，之后来的返回旧的entry//保证这把锁不管重复了几次，返回的都是同一个entryExpirationEntry oldEntry = EXPIRATION_RENEWAL_MAP.putIfAbsent(getEntryName(), entry);if (oldEntry != null) {oldEntry.addThreadId(threadId);  //同一个线程多次来获取} else {entry.addThreadId(threadId);try {renewExpiration();  //第一次来：续约，更新有效期  -->看renewExpiration} finally {if (Thread.currentThread().isInterrupted()) {cancelExpirationRenewal(threadId);}}}}
//renewExpiration：
private void renewExpiration() {  //更新有效期ExpirationEntry ee = EXPIRATION_RENEWAL_MAP.get(getEntryName());  //先得到entryif (ee == null) {return;}Timeout task = getServiceManager().newTimeout(new TimerTask() {@Overridepublic void run(Timeout timeout) throws Exception {ExpirationEntry ent = EXPIRATION_RENEWAL_MAP.get(getEntryName());  //拿出entryif (ent == null) {return;}Long threadId = ent.getFirstThreadId();  //取出线程idif (threadId == null) {return;}CompletionStage<Boolean> future = renewExpirationAsync(threadId);  //刷新有效期-->查看renewExpirationAsyncfuture.whenComplete((res, e) -> {if (e != null) {log.error("Can't update lock {} expiration", getRawName(), e);EXPIRATION_RENEWAL_MAP.remove(getEntryName());return;}if (res) {// reschedule itselfrenewExpiration();  //自己调用自己：递归--重复每十秒更新一次有效期，解决超时问题（重点！）} else {cancelExpirationRenewal(null);}});}}, internalLockLeaseTime / 3, TimeUnit.MILLISECONDS);  //内部锁施放时间/3ee.setTimeout(task);}//renewExpirationAsync：
//重置有效期protected CompletionStage<Boolean> renewExpirationAsync(long threadId) {return evalWriteAsync(getRawName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,"if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then " +//判断当前线程的锁是不是自己线程拿的--肯定能成功，不是自己线程进不来"redis.call('pexpire', KEYS[1], ARGV[1]); " +//更新有效期"return 1; " +"end; " +"return 0;",Collections.singletonList(getRawName()),internalLockLeaseTime, getLockName(threadId));}//释放锁的逻辑：
@Overridepublic void unlock() {try {get(unlockAsync(Thread.currentThread().getId()));  //查看unlockAsync} catch (RedisException e) {if (e.getCause() instanceof IllegalMonitorStateException) {throw (IllegalMonitorStateException) e.getCause();} else {throw e;}}//unlockAsync：
@Overridepublic RFuture<Void> unlockAsync(long threadId) {return getServiceManager().execute(() -> unlockAsync0(threadId));}private RFuture<Void> unlockAsync0(long threadId) {CompletionStage<Boolean> future = unlockInnerAsync(threadId);CompletionStage<Void> f = future.handle((opStatus, e) -> {cancelExpirationRenewal(threadId);  //取消更新任务 -->查看：cancelExpirationRenewalif (e != null) {if (e instanceof CompletionException) {throw (CompletionException) e;}throw new CompletionException(e);}if (opStatus == null) {IllegalMonitorStateException cause = new IllegalMonitorStateException("attempt to unlock lock, not locked by current thread by node id: "+ id + " thread-id: " + threadId);throw new CompletionException(cause);}return null;});return new CompletableFutureWrapper<>(f);}//cancelExpirationRenewal：
//定时任务的删除
protected void cancelExpirationRenewal(Long threadId) {ExpirationEntry task = EXPIRATION_RENEWAL_MAP.get(getEntryName());  //从map中取if (task == null) {return;}if (threadId != null) {task.removeThreadId(threadId);  //先把id干掉}if (threadId == null || task.hasNoThreads()) {Timeout timeout = task.getTimeout();if (timeout != null) {timeout.cancel();  //然后再把任务取消}EXPIRATION_RENEWAL_MAP.remove(getEntryName());  //最后再把entry取消掉}}

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小总结

Redisson分布式锁原理

可重入:利用hash结构记录线程id和重入次数
可重试:利用信号量和PubSub功能实现等待、唤醒，获取锁失败的重试机制
超时续约:利用watchDog，每隔一段时间(releaseTime/3)，重置超时时间

5. Redisson的multiLock原理

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RedisConfig.java：

package com.hmdp.config;import org.redisson.Redisson;
import org.redisson.api.RedissonClient;
import org.redisson.config.Config;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;@Configuration
public class RedissionConfig {@Beanpublic RedissonClient redissonClient(){// 配置类Config config =new Config();//添加redis地址，这里添加了单点的地址，也可以使用config.useClusterServers()添加集群地址config.useSingleServer().setAddress("redis://192.168.150.101:6379").setPassword("123456");// 创建客户端return Redisson.create(config);}@Beanpublic RedissonClient redissonClient2(){// 配置类Config config =new Config();//添加redis地址，这里添加了单点的地址，也可以使用config.useClusterServers()添加集群地址config.useSingleServer().setAddress("redis://192.168.150.101:6380");// 创建客户端return Redisson.create(config);}@Beanpublic RedissonClient redissonClient3(){// 配置类Config config =new Config();//添加redis地址，这里添加了单点的地址，也可以使用config.useClusterServers()添加集群地址config.useSingleServer().setAddress("redis://192.168.150.101:6381");// 创建客户端return Redisson.create(config);}
}

RedissonTest.java：

package com.hmdp;import lombok.extern.slf4j.Slf4j;
import org.junit.Test;
import org.junit.jupiter.api.BeforeEach;
import org.redisson.api.RLock;
import org.redisson.api.RedissonClient;
import org.springframework.boot.test.context.SpringBootTest;import javax.annotation.Resource;
import java.util.concurrent.TimeUnit;@Slf4j
@SpringBootTest
class RedissonTest {@Resourceprivate RedissonClient redissonClient;@Resourceprivate RedissonClient redissonClient2;@Resourceprivate RedissonClient redissonClient3;private RLock lock;@BeforeEachvoid setUp(){RLock lock1 = redissonClient.getLock("order");RLock lock2 = redissonClient2.getLock("order");RLock lock3 = redissonClient3.getLock("order");//创建联锁lock = redissonClient.getMultiLock(lock1,lock2,lock3);}@Testvoid method1() throws InterruptedException{//尝试获取锁boolean isLock = lock.tryLock(1L, TimeUnit.SECONDS);if (!isLock){log.error("获取锁失败....1");return;}try {log.info("获取锁成功....1");method2();log.info("开始执行业务....1");}finally {log.warn("准备释放锁....1");lock.unlock();}}void method2(){//尝试获取锁boolean isLock = lock.tryLock();if (!isLock){log.error("获取锁失败....2");return;}try {log.info("获取锁成功....2");log.info("开始执行业务....2");}finally {log.warn("准备释放锁....2");lock.unlock();}}
}

总结

不可重入Redis分布式锁:
原理:利用setnx的互斥性;利用ex避免死锁;释放锁时判断线程标示
缺陷:不可重入、无法重试、锁超时失效
可重入的Redis分布式锁:
原理:利用hash结构，记录线程标示和重入次数;利用watchDog延续锁时间;利用信号量控制锁重试等待
缺陷:redis宕机引起锁失效问题
Redisson的multiLock:
原理:多个独立的Redis节点，必须在所有节点都获取重入锁，才算获取锁成功
缺陷:运维成本高、实现复杂