分布式锁—5.Redisson的读写锁

大纲

1.Redisson读写锁RedissonReadWriteLock概述

2.读锁RedissonReadLock的获取读锁逻辑

3.写锁RedissonWriteLock的获取写锁逻辑

4.读锁RedissonReadLock的读读不互斥逻辑

5.RedissonReadLock和RedissonWriteLock的读写互斥逻辑

6.写锁RedissonWriteLock的写写互斥逻辑

7.写锁RedissonWriteLock的可重入逻辑

8.读锁RedissonReadLock的释放读锁逻辑

9.写锁RedissonWriteLock的释放写锁逻辑

1.Redisson读写锁RedissonReadWriteLock概述

(1)RedissonReadWriteLock的简介

(2)RedissonReadWriteLock的使用

(3)RedissonReadWriteLock的初始化

(1)RedissonReadWriteLock的简介

RedissonReadWriteLock提供了两个方法分别获取读锁和写锁。

RedissonReadWriteLock的readLock()方法可以获取读锁RedissonReadLock。

RedissonReadWriteLock的writeLock()方法可以获取写锁RedissonWriteLock。

由于RedissonReadLock和RedissonWriteLock都是RedissonLock的子类，所以只需关注RedissonReadLock和RedissonWriteLock的如下内容即可。

一是获取读锁(写锁)的lua脚本逻辑

二是释放读锁(写锁)的lua脚本逻辑

三是读锁(写锁)的WathDog检查读锁(写锁)和处理锁过期时间的逻辑

(2)RedissonReadWriteLock的使用

//读写锁
RedissonClient redisson = Redisson.create(config);
RReadWriteLock rwlock = redisson.getReadWriteLock("myLock");
rwlock.readLock().lock();//获取读锁
rwlock.readLock().unlock();//释放读锁
rwlock.writeLock().lock();//获取写锁
rwlock.writeLock().unlock();//释放写锁

---------------------------------------------------------------

//如果没有主动释放锁的话，10秒后将会自动释放锁
rwlock.readLock().lock(10, TimeUnit.SECONDS);
rwlock.writeLock().lock(10, TimeUnit.SECONDS);

//加锁等待最多是100秒；加锁成功后如果没有主动释放锁的话，锁会在10秒后自动释放
boolean res = rwlock.readLock().tryLock(100, 10, TimeUnit.SECONDS);
boolean res = rwlock.writeLock().tryLock(100, 10, TimeUnit.SECONDS);

(3)RedissonReadWriteLock的初始化

RedissonReadWriteLock实现了RReadWriteLock接口，RedissonReadLock实现了RLock接口，RedissonWriteLock实现了RLock接口。

public class Redisson implements RedissonClient {
    //Redis的连接管理器，封装了一个Config实例
    protected final ConnectionManager connectionManager;
    //Redis的命令执行器，封装了一个ConnectionManager实例
    protected final CommandAsyncExecutor commandExecutor;
    ...
    
    protected Redisson(Config config) {
        this.config = config;
        Config configCopy = new Config(config);
        //初始化Redis的连接管理器
        connectionManager = ConfigSupport.createConnectionManager(configCopy);
        ...  
        //初始化Redis的命令执行器
        commandExecutor = new CommandSyncService(connectionManager, objectBuilder);
        ...
    }
    
    @Override
    public RReadWriteLock getReadWriteLock(String name) {
        return new RedissonReadWriteLock(commandExecutor, name);
    }
    ...
}

public class RedissonReadWriteLock extends RedissonExpirable implements RReadWriteLock {
    public RedissonReadWriteLock(CommandAsyncExecutor commandExecutor, String name) {
        super(commandExecutor, name);
    }
    
    @Override
    public RLock readLock() {
        return new RedissonReadLock(commandExecutor, getRawName());
    }
    
    @Override
    public RLock writeLock() {
        return new RedissonWriteLock(commandExecutor, getRawName());
    }
}

public class RedissonReadLock extends RedissonLock implements RLock {
    public RedissonReadLock(CommandAsyncExecutor commandExecutor, String name) {
        super(commandExecutor, name);
    }
    ...
}

public class RedissonWriteLock extends RedissonLock implements RLock {
    protected RedissonWriteLock(CommandAsyncExecutor commandExecutor, String name) {
        super(commandExecutor, name);
    }
    ...
}

2.读锁RedissonReadLock的获取读锁逻辑

(1)加读锁的lua脚本逻辑

(2)WathDog处理读锁过期时间的lua脚本逻辑

(1)加读锁的lua脚本逻辑

假设客户端A的线程(UUID1:ThreadID1)作为第一个线程进来加读锁，执行流程如下：

public class RedissonLock extends RedissonBaseLock {
    ...
    //不带参数的加锁
    public void lock() {
        ...
        lock(-1, null, false);
        ...
    }
    
    //带参数的加锁
    public void lock(long leaseTime, TimeUnit unit) {
        ...
       lock(leaseTime, unit, false);
        ...
    }
    
    private void lock(long leaseTime, TimeUnit unit, boolean interruptibly) throws InterruptedException {
        long threadId = Thread.currentThread().getId();
        Long ttl = tryAcquire(-1, leaseTime, unit, threadId);
        //加锁成功
        if (ttl == null) {
            return;
        }
        //加锁失败
        ...
    }
    
    private Long tryAcquire(long waitTime, long leaseTime, TimeUnit unit, long threadId) {
        return get(tryAcquireAsync(waitTime, leaseTime, unit, threadId));
    }
    
    private <T> RFuture<Long> tryAcquireAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId) {
        RFuture<Long> ttlRemainingFuture;
        if (leaseTime != -1) {
            ttlRemainingFuture = tryLockInnerAsync(waitTime, leaseTime, unit, threadId, RedisCommands.EVAL_LONG);
        } else {
            //非公平锁，接下来调用的是RedissonLock.tryLockInnerAsync()方法
            //公平锁，接下来调用的是RedissonFairLock.tryLockInnerAsync()方法
            //读写锁中的读锁，接下来调用RedissonReadLock.tryLockInnerAsync()方法
            ttlRemainingFuture = tryLockInnerAsync(waitTime, internalLockLeaseTime, TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);
        }
      
        //对RFuture<Long>类型的ttlRemainingFuture添加回调监听
        CompletionStage<Long> f = ttlRemainingFuture.thenApply(ttlRemaining -> {
            //tryLockInnerAsync()里的加锁lua脚本异步执行完毕，会回调如下方法逻辑：
            //加锁成功
            if (ttlRemaining == null) {
                if (leaseTime != -1) {
                    //如果传入的leaseTime不是-1，也就是指定锁的过期时间，那么就不创建定时调度任务
                    internalLockLeaseTime = unit.toMillis(leaseTime);
                } else {
                    //创建定时调度任务
                    scheduleExpirationRenewal(threadId);
                }
            }
            return ttlRemaining;
        });
        return new CompletableFutureWrapper<>(f);
    }
    ...
}

public class RedissonReadLock extends RedissonLock implements RLock {
    ...
    @Override
    <T> RFuture<T> tryLockInnerAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,
            //执行命令"hget myLock mode"，尝试获取一个Hash值mode
            "local mode = redis.call('hget', KEYS[1], 'mode'); " +
            //mode为false则执行加读锁的逻辑
            "if (mode == false) then " +
                //hset myLock mode read
                "redis.call('hset', KEYS[1], 'mode', 'read'); " +
                //hset myLock UUID1:ThreadID1 1
                "redis.call('hset', KEYS[1], ARGV[2], 1); " +
                //set {myLock}:UUID1:ThreadID1:rwlock_timeout:1 1
                "redis.call('set', KEYS[2] .. ':1', 1); " +
                //pexpire {myLock}:UUID1:ThreadID1:rwlock_timeout:1 30000
                "redis.call('pexpire', KEYS[2] .. ':1', ARGV[1]); " +
                //pexpire myLock 30000
                "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                "return nil; " +
            "end; " +
            //如果已经有线程加了读锁 或者 有线程加了写锁且是自己加的写锁
            //所以一个线程如果加了写锁，它是可以重入自己的写锁和自己的读锁的
            "if (mode == 'read') or (mode == 'write' and redis.call('hexists', KEYS[1], ARGV[3]) == 1) then " +
                //hincrby myLock UUID2:ThreadID2 1
                //ind表示重入次数，线程可以重入自己的读锁和写锁，线程后加的读锁可以重入线程自己的读锁或写锁
                "local ind = redis.call('hincrby', KEYS[1], ARGV[2], 1); " + 
                //key = {myLock}:UUID2:ThreadID2:rwlock_timeout:1
                "local key = KEYS[2] .. ':' .. ind;" +
                //set {myLock}:UUID2:ThreadID2:rwlock_timeout:1 1
                "redis.call('set', key, 1); " +
                //pexpire myLock 30000
                "redis.call('pexpire', key, ARGV[1]); " +
                "local remainTime = redis.call('pttl', KEYS[1]); " +
                //pexpire {myLock}:UUID2:ThreadID2:rwlock_timeout:1 30000
                "redis.call('pexpire', KEYS[1], math.max(remainTime, ARGV[1])); " +
                "return nil; " +
            "end;" +
            //执行命令"pttl myLock"，返回myLock的剩余过期时间
            "return redis.call('pttl', KEYS[1]);",
            //KEYS[1] = myLock
            //KEYS[2] = {myLock}:UUID1:ThreadID1:rwlock_timeout 或 KEYS[2] = {myLock}:UUID2:ThreadID2:rwlock_timeout
            Arrays.<Object>asList(getRawName(), getReadWriteTimeoutNamePrefix(threadId)),
            unit.toMillis(leaseTime),//ARGV[1] = 30000
            getLockName(threadId),//ARGV[2] = UUID1:ThreadID1 或 ARGV[2] = UUID2:ThreadID2
            getWriteLockName(threadId)//ARGV[3] = UUID1:ThreadID1:write 或 ARGV[3] = UUID2:ThreadID2:write
        );
    }
    ...
}

一.参数说明

KEYS[1] = myLock
KEYS[2] = {myLock}:UUID1:ThreadID1:rwlock_timeout
ARGV[1] = 30000
ARGV[2] = UUID1:ThreadID1
ARGV[3] = UUID1:ThreadID1:write

二.执行lua脚本的获取读锁逻辑

首先执行命令"hget myLock mode"，尝试获取一个Hash值mode，也就是从key为myLock的Hash值里获取一个field为mode的value值。但是此时一开始都还没有加锁，所以mode肯定是false。于是就执行如下加读锁的逻辑：设置两个Hash值 + 设置一个字符串。

hset myLock mode read
//用来记录当前客户端线程重入锁的次数
hset myLock UUID1:ThreadID1 1
//用来记录当前客户端线程第1个重入锁过期时间
set {myLock}:UUID1:ThreadID1:rwlock_timeout:1 1
pexpire {myLock}:UUID1:ThreadID1:rwlock_timeout:1 30000
pexpire myLock 30000

执行完加读锁逻辑后，Redis存在如下结构的数据。其实加读锁的核心在于构造一个递增序列，记录不同线程的读锁和同一个线程不同的重入锁。

field为类似于UUID1:ThreadID1的value值，是用来记录当前客户端线程重入锁次数的。key为类似于{myLock}:UUID1:ThreadID1:rwlock_timeout:1的String，是用来记录当前客户端线程第n个重入锁过期时间的。

假设将key为myLock称为父读锁，key为UUID1:ThreadID1称为子读锁。那么记录每一个子读锁的过期时间，是因为需要根据多个子读锁的过期时间更新父读锁的过期时间。

//1.线程1第一次加读锁
//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 1
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1

//2.线程1第二次加读锁
//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 2
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:2 ==> 1

//3.线程1第三次加读锁
//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 3
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:2 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:3 ==> 1

//4.线程2第一次加读锁
//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 3,
    "UUID2:ThreadID2": 1
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:2 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:3 ==> 1
{myLock}:UUID2:ThreadID2:rwlock_timeout:1 ==> 1

//5.线程2第二次加读锁
//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 3,
    "UUID2:ThreadID2": 2
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:2 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:3 ==> 1
{myLock}:UUID2:ThreadID2:rwlock_timeout:1 ==> 1
{myLock}:UUID2:ThreadID2:rwlock_timeout:2 ==> 1

(2)WathDog处理读锁过期时间的lua脚本逻辑

假设客户端A的线程(UUID1:ThreadID1)已经成功获取到一个读锁，此时会创建一个WatchDog定时调度任务，10秒后检查该读锁。执行流程如下：

public abstract class RedissonBaseLock extends RedissonExpirable implements RLock {
    ...
    protected void scheduleExpirationRenewal(long threadId) {
        ExpirationEntry entry = new ExpirationEntry();
        ExpirationEntry oldEntry = EXPIRATION_RENEWAL_MAP.putIfAbsent(getEntryName(), entry);
        if (oldEntry != null) {
            oldEntry.addThreadId(threadId);
        } else {
            entry.addThreadId(threadId);
            try {
                //创建一个更新过期时间的定时调度任务
                renewExpiration();
            } finally {
                if (Thread.currentThread().isInterrupted()) {
                    cancelExpirationRenewal(threadId);
                }
            }
        }
    }
    
    //更新过期时间
    private void renewExpiration() {
        ExpirationEntry ee = EXPIRATION_RENEWAL_MAP.get(getEntryName());
        if (ee == null) {
            return;
        }
        //使用了Netty的定时任务机制：HashedWheelTimer + TimerTask + Timeout
        //创建一个更新过期时间的定时调度任务，下面会调用MasterSlaveConnectionManager.newTimeout()方法
        //即创建一个定时调度任务TimerTask交给HashedWheelTimer，10秒后执行
        Timeout task = commandExecutor.getConnectionManager().newTimeout(new TimerTask() {
            @Override
            public void run(Timeout timeout) throws Exception {
                ExpirationEntry ent = EXPIRATION_RENEWAL_MAP.get(getEntryName());
                if (ent == null) {
                    return;
                }
                Long threadId = ent.getFirstThreadId();
                if (threadId == null) {
                    return;
                }
                //异步执行lua脚本去更新锁的过期时间
                //对于读写锁，接下来会执行RedissonReadLock.renewExpirationAsync()方法
                RFuture<Boolean> future = renewExpirationAsync(threadId);
                future.whenComplete((res, e) -> {
                    if (e != null) {
                        log.error("Can't update lock " + getRawName() + " expiration", e);
                        EXPIRATION_RENEWAL_MAP.remove(getEntryName());
                        return;
                    }
                    //res就是执行renewExpirationAsync()里的lua脚本的返回值
                    if (res) {
                        //重新调度自己
                        renewExpiration();
                    } else {
                        //执行清理工作
                        cancelExpirationRenewal(null);
                    }
                });
            }
        }, internalLockLeaseTime / 3, TimeUnit.MILLISECONDS);
        ee.setTimeout(task);
    }
    
    protected void cancelExpirationRenewal(Long threadId) {
        ExpirationEntry task = EXPIRATION_RENEWAL_MAP.get(getEntryName());
        if (task == null) {
            return;
        }
        if (threadId != null) {
            task.removeThreadId(threadId);
        }
        if (threadId == null || task.hasNoThreads()) {
            Timeout timeout = task.getTimeout();
            if (timeout != null) {
                timeout.cancel();
            }
            EXPIRATION_RENEWAL_MAP.remove(getEntryName());
        }
    }
    ...
}

public class RedissonReadLock extends RedissonLock implements RLock {
    ...
    @Override
    protected RFuture<Boolean> renewExpirationAsync(long threadId) {
        String timeoutPrefix = getReadWriteTimeoutNamePrefix(threadId);
        String keyPrefix = getKeyPrefix(threadId, timeoutPrefix);
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,
            //执行命令"hget myLock UUID1:ThreadID1"，获取当前这个线程是否还持有这个读锁
            "local counter = redis.call('hget', KEYS[1], ARGV[2]); " +
            "if (counter ~= false) then " +
                //指定的线程还在持有锁，那么就执行"pexpire myLock 30000"刷新锁的过期时间
                "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                "if (redis.call('hlen', KEYS[1]) > 1) then " +
                    //获取key为myLock的Hash值的所有key
                    "local keys = redis.call('hkeys', KEYS[1]); " + 
                    //遍历已被线程获取的所有重入和非重入的读锁
                    "for n, key in ipairs(keys) do " + 
                        "counter = tonumber(redis.call('hget', KEYS[1], key)); " + 
                        //排除掉key为mode的Hash值
                        "if type(counter) == 'number' then " + 
                            //递减拼接重入锁的key，刷新同一个线程的所有重入锁的过期时间
                            "for i=counter, 1, -1 do " + 
                                "redis.call('pexpire', KEYS[2] .. ':' .. key .. ':rwlock_timeout:' .. i, ARGV[1]); " + 
                            "end; " + 
                        "end; " + 
                    "end; " +
                "end; " +
                "return 1; " +
            "end; " +
            "return 0;",
            //KEYS[1] = myLock
            //KEYS[2] = {myLock}
            Arrays.<Object>asList(getRawName(), keyPrefix),
            internalLockLeaseTime,//ARGV[1] = 30000毫秒
            getLockName(threadId)//ARGV[2] = UUID1:ThreadID1
        );
    }
    ...
}

一.参数说明

KEYS[1] = myLock
KEYS[2] = {myLock}
ARGV[1] = 30000
ARGV[2] = UUID1:ThreadID1

二.执行lua脚本的处理逻辑

执行命令"hget myLock UUID1:ThreadID1"，尝试获取一个Hash值，也就是获取指定的这个线程是否还持有这个读锁。如果指定的这个线程还在持有这个锁，那么这里返回的是1，于是就会执行"pexpire myLock 30000"刷新锁的过期时间。

接着执行命令"hlen myLock"，判断key为锁名的Hash元素个数是否大于1。如果指定的这个线程还在持有这个锁，那么key为myLock的Hash值就至少有两个kv对。其中一个key是mode，一个key是UUID1:ThreadID1。所以这里的判断是成立的，于是遍历处理key为锁名的Hash值。

在遍历处理key为锁名的Hash值时，需要排除掉key为mode的Hash值。然后根据key为UUID + 线程ID的Hash值，通过递减拼接，进行循环遍历，把每一个不同线程的读锁或同一个线程不同的重入锁，都刷新过期时间。

三.总结

WatchDog在处理读锁时，如果指定的线程还持有读锁，那么就会：刷新读锁key的过期时间为30秒，根据重入读锁的次数进行遍历，对重入读锁对应的key的过期时间也刷新为30秒。

//KEYS[1] = myLock
//KEYS[2] = {myLock}
"if (redis.call('hlen', KEYS[1]) > 1) then " +
    "local keys = redis.call('hkeys', KEYS[1]); " + 
    //遍历处理key为锁名的Hash值
    "for n, key in ipairs(keys) do " + 
        "counter = tonumber(redis.call('hget', KEYS[1], key)); " + 
        //排除掉key为mode的Hash值
        "if type(counter) == 'number' then " + 
            "for i=counter, 1, -1 do " + 
                //递减拼接，把不同线程的读锁或同一个线程不同的重入锁，都刷新过期时间
                "redis.call('pexpire', KEYS[2] .. ':' .. key .. ':rwlock_timeout:' .. i, ARGV[1]); " + 
            "end; " + 
        "end; " + 
    "end; " +
"end; " +

//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 3,
    "UUID2:ThreadID2": 2
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:2 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:3 ==> 1
{myLock}:UUID2:ThreadID2:rwlock_timeout:1 ==> 1
{myLock}:UUID2:ThreadID2:rwlock_timeout:2 ==> 1

3.写锁RedissonWriteLock的获取写锁逻辑

(1)获取写锁的执行流程

(2)获取写锁的lua脚本逻辑

(1)获取写锁的执行流程

假设客户端A的线程(UUID1:ThreadID1)作为第一个线程进来加写锁，执行流程如下：

public class RedissonLock extends RedissonBaseLock {
    ...
    //不带参数的加锁
    public void lock() {
        ...
        lock(-1, null, false);
        ...
    }
    
    //带参数的加锁
    public void lock(long leaseTime, TimeUnit unit) {
        ...
        lock(leaseTime, unit, false);
        ...
    }
    
    private void lock(long leaseTime, TimeUnit unit, boolean interruptibly) throws InterruptedException {
        long threadId = Thread.currentThread().getId();
        Long ttl = tryAcquire(-1, leaseTime, unit, threadId);
        //加锁成功
        if (ttl == null) {
            return;
        }
        //加锁失败
        ...
    }
    
    private Long tryAcquire(long waitTime, long leaseTime, TimeUnit unit, long threadId) {
        return get(tryAcquireAsync(waitTime, leaseTime, unit, threadId));
    }
    
    private <T> RFuture<Long> tryAcquireAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId) {
        RFuture<Long> ttlRemainingFuture;
        if (leaseTime != -1) {
            ttlRemainingFuture = tryLockInnerAsync(waitTime, leaseTime, unit, threadId, RedisCommands.EVAL_LONG);
        } else {
            //非公平锁，接下来调用的是RedissonLock.tryLockInnerAsync()方法
            //公平锁，接下来调用的是RedissonFairLock.tryLockInnerAsync()方法
            //读写锁中的读锁，接下来调用RedissonReadLock.tryLockInnerAsync()方法
            //读写锁中的写锁，接下来调用RedissonWriteLock.tryLockInnerAsync()方法
            ttlRemainingFuture = tryLockInnerAsync(waitTime, internalLockLeaseTime, TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);
        }
        //对RFuture<Long>类型的ttlRemainingFuture添加回调监听
        CompletionStage<Long> f = ttlRemainingFuture.thenApply(ttlRemaining -> {
            //tryLockInnerAsync()里的加锁lua脚本异步执行完毕，会回调如下方法逻辑：
            //加锁成功
            if (ttlRemaining == null) {
                if (leaseTime != -1) {
                    //如果传入的leaseTime不是-1，也就是指定锁的过期时间，那么就不创建定时调度任务
                    internalLockLeaseTime = unit.toMillis(leaseTime);
                } else {
                    //创建定时调度任务
                    scheduleExpirationRenewal(threadId);
                }
            }
            return ttlRemaining;
        });
        return new CompletableFutureWrapper<>(f);
    }
    ...
}

public class RedissonWriteLock extends RedissonLock implements RLock {
    ...
    @Override
    <T> RFuture<T> tryLockInnerAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,
            //执行命令"hget myLock mode"，尝试获取一个Hash值mode
            "local mode = redis.call('hget', KEYS[1], 'mode'); " +
            //获取不到，说明没有加读锁或者写锁
            "if (mode == false) then " +
                "redis.call('hset', KEYS[1], 'mode', 'write'); " +
                "redis.call('hset', KEYS[1], ARGV[2], 1); " +
                "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                "return nil; " +
            "end; " +
            //如果加过锁，那么就要看是不是写锁 + 写锁是不是自己加过的(即重入写锁)
            "if (mode == 'write') then " +
                "if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then " +
                    //重入写锁
                    "redis.call('hincrby', KEYS[1], ARGV[2], 1); " + 
                    "local currentExpire = redis.call('pttl', KEYS[1]); " +
                    "redis.call('pexpire', KEYS[1], currentExpire + ARGV[1]); " +
                    "return nil; " +
                "end; " +
            "end;" +
            //执行命令"pttl myLock"，返回myLock的剩余过期时间
            "return redis.call('pttl', KEYS[1]);",
            Arrays.<Object>asList(getRawName()),//KEYS[1] = myLock
            unit.toMillis(leaseTime),//ARGV[1] = 30000
            getLockName(threadId)//ARGV[2] = UUID1:ThreadID1:write
        );
    }
    ...
}

(2)获取写锁的lua脚本逻辑

一.参数说明

KEYS[1] = myLock
ARGV[1] = 30000
ARGV[2] = UUID1:ThreadID1:write

二.执行分析

首先执行命令"hget myLock mode"，尝试获取一个Hash值mode，也就是从key为myLock的Hash值里获取一个field为mode的value值。但是此时一开始都还没有加锁，所以mode肯定是false。于是就执行如下加读锁的逻辑：设置两个Hash值。

hset myLock mode write
hset myLock UUID1:ThreadID1:write 1
pexpire myLock 30000

完成加锁操作后，Redis中存在如下数据：

//Hash结构
myLock: {
    "mode": "write",
    "UUID1:ThreadID1:write": 1
}

4.读锁RedissonReadLock的读读不互斥逻辑

(1)不同客户端线程读锁与读锁不互斥说明

(2)客户端A先加读锁的Redis命令执行过程和结果

(3)客户端B后加读锁的Redis命令执行过程和结果

(1)不同客户端线程读锁与读锁不互斥说明

假设客户端A(UUID1:ThreadID1)对myLock这个锁先加了一个读锁，客户端B(UUID2:ThreadID2)也要对myLock这个锁加一个读锁，那么此时这两个读锁是不会互斥的，客户端B可以加锁成功。

public class RedissonReadLock extends RedissonLock implements RLock {
    ...
    @Override
    <T> RFuture<T> tryLockInnerAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,
            //执行命令"hget myLock mode"，尝试获取一个Hash值mode
            "local mode = redis.call('hget', KEYS[1], 'mode'); " +
            //mode为false则执行加读锁的逻辑
            "if (mode == false) then " +
                //hset myLock mode read
                "redis.call('hset', KEYS[1], 'mode', 'read'); " +
                //hset myLock UUID1:ThreadID1 1
                "redis.call('hset', KEYS[1], ARGV[2], 1); " +
                //set {myLock}:UUID1:ThreadID1:rwlock_timeout:1 1
                "redis.call('set', KEYS[2] .. ':1', 1); " +
                //pexpire {myLock}:UUID1:ThreadID1:rwlock_timeout:1 30000
                "redis.call('pexpire', KEYS[2] .. ':1', ARGV[1]); " +
                //pexpire myLock 30000
                "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                "return nil; " +
            "end; " +
            //如果已经有线程加了读锁 或者 有线程加了写锁且是自己加的写锁
            //所以一个线程如果加了写锁，它是可以重入自己的写锁和自己的读锁的
            "if (mode == 'read') or (mode == 'write' and redis.call('hexists', KEYS[1], ARGV[3]) == 1) then " +
                //hincrby myLock UUID2:ThreadID2 1
                //ind表示重入次数，线程可以重入自己的读锁和写锁，线程后加的读锁可以重入线程自己的读锁或写锁
                "local ind = redis.call('hincrby', KEYS[1], ARGV[2], 1); " + 
                //key = {myLock}:UUID2:ThreadID2:rwlock_timeout:1
                "local key = KEYS[2] .. ':' .. ind;" +
                //set {myLock}:UUID2:ThreadID2:rwlock_timeout:1 1
                "redis.call('set', key, 1); " +
                //pexpire myLock 30000
                "redis.call('pexpire', key, ARGV[1]); " +
                "local remainTime = redis.call('pttl', KEYS[1]); " +
                //pexpire {myLock}:UUID2:ThreadID2:rwlock_timeout:1 30000
                "redis.call('pexpire', KEYS[1], math.max(remainTime, ARGV[1])); " +
                "return nil; " +
            "end;" +
            //执行命令"pttl myLock"，返回myLock的剩余过期时间
            "return redis.call('pttl', KEYS[1]);",
            //KEYS[1] = myLock
            //KEYS[2] = {myLock}:UUID1:ThreadID1:rwlock_timeout 或 KEYS[2] = {myLock}:UUID2:ThreadID2:rwlock_timeout
            Arrays.<Object>asList(getRawName(), getReadWriteTimeoutNamePrefix(threadId)),
            unit.toMillis(leaseTime),//ARGV[1] = 30000
            getLockName(threadId),//ARGV[2] = UUID1:ThreadID1 或 ARGV[2] = UUID2:ThreadID2
            getWriteLockName(threadId)//ARGV[3] = UUID1:ThreadID1:write 或 ARGV[3] = UUID2:ThreadID2:write
        );
    }
    ...
}

(2)客户端A先加读锁的Redis命令执行过程和结果

参数说明：

KEYS[1] = myLock
KEYS[2] = {myLock}:UUID1:ThreadID1:rwlock_timeout
ARGV[1] = 30000
ARGV[2] = UUID1:ThreadID1
ARGV[3] = UUID1:ThreadID1:write

Redis命令的执行过程：

hset myLock mode read
hset myLock UUID1:ThreadID1 1
set {myLock}:UUID1:ThreadID1:rwlock_timeout:1 1
pexpire {myLock}:UUID1:ThreadID1:rwlock_timeout:1 30000
pexpire myLock 30000

Redis执行结果：

//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 1
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1

(3)客户端B后加读锁的Redis命令执行过程和结果

参数说明：

KEYS[1] = myLock
KEYS[2] = {myLock}:UUID2:ThreadID2:rwlock_timeout 
ARGV[1] = 30000
ARGV[2] = UUID2:ThreadID2
ARGV[3] = UUID2:ThreadID2:write

Redis命令的执行过程：

hget myLock mode ===> 获取到mode=read，表示此时已经有线程加了读锁
hincrby myLock UUID2:ThreadID2 1
set {myLock}:UUID2:ThreadID2:rwlock_timeout:1 1
pexpire myLock 30000
pexpire {myLock}:UUID2:ThreadID2:rwlock_timeout:1 30000

Redis执行结果：

//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 1,
    "UUID2:ThreadID2": 1
}

//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID2:ThreadID2:rwlock_timeout:1 ==> 1

需要注意的是：多个客户端同时加读锁，读锁与读锁不互斥。会不断在key为锁名的Hash里，自增field为客户端UUID + 线程ID的value值。每个客户端成功加的一次读锁或写锁，都会维持一个WatchDog，不断刷新myLock的生存时间 + 刷新该客户端这次加的锁的过期时间。

加读锁的lua脚本中，ind表示重入次数。线程可重入自己的读锁和写锁。也就是说，线程后加的读锁可以重入线程自己先加的读锁或写锁。

5.RedissonReadLock和RedissonWriteLock的读写互斥逻辑

(1)不同客户端线程先读锁后写锁如何互斥

(2)不同客户端线程先写锁后读锁如何互斥

(1)不同客户端线程先读锁后写锁如何互斥

首先，客户端A(UUID1:ThreadID1)和客户端B(UUID2:ThreadID2)先加读锁，此时Redis中存在如下的数据：

//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 1,
    "UUID2:ThreadID2": 1
}

//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID2:ThreadID2:rwlock_timeout:1 ==> 1

接着，客户端C(UUID3:ThreadID3)来加写锁。

public class RedissonWriteLock extends RedissonLock implements RLock {
    ...
    @Override
    <T> RFuture<T> tryLockInnerAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,
            //执行命令"hget myLock mode"，尝试获取一个Hash值mode
            "local mode = redis.call('hget', KEYS[1], 'mode'); " +
            //此时发现mode=read，说明已有线程加了锁了
            "if (mode == false) then " +
                "redis.call('hset', KEYS[1], 'mode', 'write'); " +
                "redis.call('hset', KEYS[1], ARGV[2], 1); " +
                "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                "return nil; " +
            "end; " +
            //如果加过锁，那么就要看是不是写锁 + 写锁是不是自己加过的(即重入写锁)
            "if (mode == 'write') then " +
                "if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then " +
                    //重入写锁
                    "redis.call('hincrby', KEYS[1], ARGV[2], 1); " + 
                    "local currentExpire = redis.call('pttl', KEYS[1]); " +
                    "redis.call('pexpire', KEYS[1], currentExpire + ARGV[1]); " +
                    "return nil; " +
                "end; " +
            "end;" +
            //执行命令"pttl myLock"，返回myLock的剩余过期时间
            "return redis.call('pttl', KEYS[1]);",
            Arrays.<Object>asList(getRawName()),//KEYS[1] = myLock
            unit.toMillis(leaseTime),//ARGV[1] = 30000
            getLockName(threadId)//ARGV[2] = UUID3:ThreadID3:write
        );
    }
    ...
}

客户端C(UUID3:ThreadID3)加写锁时的参数：

KEYS[1] = myLock
ARGV[1] = 30000
ARGV[2] = UUID3:ThreadID3:write

客户端C(UUID3:ThreadID3)加写锁时：首先执行命令"hget myLock mode"发现mode = read，说明已有线程加了锁了。由于已加的锁不是当前线程加的写锁，而是其他线程加的读锁。所以此时会执行命令"pttl myLock"，返回myLock的剩余过期时间。这会导致客户端C加锁失败，会在while循环中阻塞和重试，从而实现先读锁后写锁的互斥。

(2)不同客户端线程先写锁后读锁如何互斥

假设客户端A(UUID1:ThreadID1)先加了一个写锁，此时Redis中存在如下的数据：

//Hash结构
myLock: {
    "mode": "write",
    "UUID1:ThreadID1:write": 1
}

然后客户端B(UUID2:ThreadID2)再来加读锁。

public class RedissonReadLock extends RedissonLock implements RLock {
    ...
    @Override
    <T> RFuture<T> tryLockInnerAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,
            //执行命令"hget myLock mode"，尝试获取一个Hash值mode
            "local mode = redis.call('hget', KEYS[1], 'mode'); " +
            //发现mode=write，说明已有线程加了锁了
            "if (mode == false) then " +
                "redis.call('hset', KEYS[1], 'mode', 'read'); " +
                "redis.call('hset', KEYS[1], ARGV[2], 1); " +
                "redis.call('set', KEYS[2] .. ':1', 1); " +
                "redis.call('pexpire', KEYS[2] .. ':1', ARGV[1]); " +
                "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                "return nil; " +
            "end; " +
            //如果已经有线程加了读锁 或者 有线程加了写锁且是自己加的写锁
            //所以一个线程如果加了写锁，它是可以重入自己的写锁和自己的读锁的
            "if (mode == 'read') or (mode == 'write' and redis.call('hexists', KEYS[1], ARGV[3]) == 1) then " +
                //hincrby myLock UUID2:ThreadID2 1
                //ind表示重入次数，线程可以重入自己的读锁和写锁，线程后加的读锁可以重入线程自己的读锁或写锁
                "local ind = redis.call('hincrby', KEYS[1], ARGV[2], 1); " + 
                //key = {myLock}:UUID2:ThreadID2:rwlock_timeout:1
                "local key = KEYS[2] .. ':' .. ind;" +
                //set {myLock}:UUID2:ThreadID2:rwlock_timeout:1 1
                "redis.call('set', key, 1); " +
                //pexpire myLock 30000
                "redis.call('pexpire', key, ARGV[1]); " +
                "local remainTime = redis.call('pttl', KEYS[1]); " +
                //pexpire {myLock}:UUID2:ThreadID2:rwlock_timeout:1 30000
                "redis.call('pexpire', KEYS[1], math.max(remainTime, ARGV[1])); " +
                "return nil; " +
            "end;" +
            //执行命令"pttl myLock"，返回myLock的剩余过期时间
            "return redis.call('pttl', KEYS[1]);",
            //KEYS[1] = myLock
            //KEYS[2] = {myLock}:UUID2:ThreadID2:rwlock_timeout
            Arrays.<Object>asList(getRawName(), getReadWriteTimeoutNamePrefix(threadId)),
            unit.toMillis(leaseTime),//ARGV[1] = 30000
            getLockName(threadId),//ARGV[2] = UUID2:ThreadID2
            getWriteLockName(threadId)//ARGV[3] = UUID2:ThreadID2:write
        );
    }
    ...
}

客户端B(UUID2:ThreadID2)加读锁时的参数：

KEYS[1] = myLock
KEYS[2] = {myLock}:UUID2:ThreadID2:rwlock_timeout 
ARGV[1] = 30000
ARGV[2] = UUID2:ThreadID2
ARGV[3] = UUID2:ThreadID2:write

客户端B(UUID2:ThreadID2)加读锁时：首先执行命令"hget myLock mode"发现mode = write，说明已有线程加了锁了。接下来执行命令"hexists myLock UUID2:ThreadID2:write"，发现不存在。也就是说，如果客户端B之前加过写锁，此时B加读锁才能通过判断。但是，之前加写锁的是客户端A，所以这里的判断条件不会通过。于是返回"pttl myLock"，导致加读锁失败，会在while循环中阻塞和重试，从而实现先写锁后读锁的互斥。

(3)总结

如果客户端线程A之前先加了写锁，此时该线程再加读锁，可以成功。

如果客户端线程A之前先加了写锁，此时该线程再加写锁，可以成功。

如果客户端线程A之前先加了读锁，此时该线程再加读锁，可以成功。

如果客户端线程A之前先加了读锁，此时该线程再加写锁，不可以成功。

所以写锁可以被自己的写锁重入，也可以被自己的读锁重入。但是读锁可以被任意的读锁重入，不可以被任意的写锁重入。

6.写锁RedissonWriteLock的写写互斥逻辑

(1)不同客户端线程先加写锁的情况

(2)不同客户端线程再加写锁的情况

(1)不同客户端线程先加写锁的情况

假设客户端A(UUID1:ThreadID1)先加写锁：

//传入参数
KEYS[1] = myLock
ARGV[1] = 30000
ARGV[2] = UUID1:ThreadID1:write

//执行结果
myLock: {
    "mode": "write",
    "UUID1:ThreadID1:write": 1
}

(2)不同客户端线程再加写锁的情况

假设客户端B(UUID2:ThreadID2)再加写锁：首先执行命令"hget myLock mode"发现mode = write，说明已有线程加了写锁。然后继续执行命令"hexists myLock UUID2:ThreadID2:write"，判断已加的写锁是否是当前客户端B(UUID2:ThreadID2)加的。由于已加的写锁是客户端A(UUID1:ThreadID1)加的，所以判断不通过。于是执行"pttl myLock"返回myLock的剩余过期时间。这样会导致客户端B加写锁失败，于是会在while循环阻塞和重试加写锁，从而实现不同客户端线程的写锁和写锁的互斥。

public class RedissonWriteLock extends RedissonLock implements RLock {
    ...
    @Override
    <T> RFuture<T> tryLockInnerAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,
            //执行命令"hget myLock mode"，尝试获取一个Hash值mode
            "local mode = redis.call('hget', KEYS[1], 'mode'); " +
            //获取不到，说明没有加读锁或者写锁
            "if (mode == false) then " +
                "redis.call('hset', KEYS[1], 'mode', 'write'); " +
                "redis.call('hset', KEYS[1], ARGV[2], 1); " +
                "redis.call('pexpire', KEYS[1], ARGV[1]); " +
                "return nil; " +
            "end; " +
            //如果加过锁，那么就要看是不是写锁+写锁是不是自己加过的(即重入写锁)
            "if (mode == 'write') then " +
                "if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then " +
                    //重入写锁
                    "redis.call('hincrby', KEYS[1], ARGV[2], 1); " + 
                    "local currentExpire = redis.call('pttl', KEYS[1]); " +
                    "redis.call('pexpire', KEYS[1], currentExpire + ARGV[1]); " +
                    "return nil; " +
                "end; " +
            "end;" +
            //执行命令"pttl myLock"，返回myLock的剩余过期时间
            "return redis.call('pttl', KEYS[1]);",
            Arrays.<Object>asList(getRawName()),//KEYS[1] = myLock
            unit.toMillis(leaseTime),//ARGV[1] = 30000
            getLockName(threadId)//ARGV[2] = UUID1:ThreadID1:write 或 ARGV[2] = UUID2:ThreadID2:write
        );
    }
    ...
}

7.写锁RedissonWriteLock的可重入逻辑

(1)同一个客户端线程先加读锁再加读锁

(2)同一个客户端线程先加读锁再加写锁

(3)同一个客户端线程先加写锁再加读锁

(4)同一个客户端线程先加写锁再加写锁

前面分析了不同客户端线程的四种加锁情况：

情况一：先加读锁再加读锁，不互斥

情况二：先加读锁再加写锁，互斥

情况三：先加写锁再加读锁，互斥

情况四：先加写锁再加写锁，互斥

接下来分析同一个客户端线程的四种加锁情况：

情况一：先加读锁再加读锁，不互斥

情况二：先加读锁再加写锁，互斥

情况三：先加写锁再加读锁，不互斥

情况四：先加写锁再加写锁，不互斥

可以这样理解：写锁优先级高，读锁优先级低。同一个线程如果先加了优先级高的写锁，那就可以继续加优先级低的读锁。同一个线程如果先加了优先级低的读锁，那就不可以再加优先级高的写锁。一般锁可以降级，不可以升级。

(1)同一个客户端线程先加读锁再加读锁

客户端A(UUID1:ThreadID1)先加了一次读锁时：

//传入参数
KEYS[1] = myLock
KEYS[2] = {myLock}:UUID1:ThreadID1:rwlock_timeout 

ARGV[1] = 30000
ARGV[2] = UUID1:ThreadID1
ARGV[3] = UUID1:ThreadID1:write

//执行结果
//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 1
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1

客户端A(UUID1:ThreadID1)再加一次读锁时，判断通过可以加成功。

//执行命令
hget myLock mode，发现mode=read，表示已经加过读锁
hincrby myLock UUID1:ThreadID1 1
set {myLock}:UUID1:ThreadID1:rwlock_timeout:2 1
pexpire myLock 30000
pexpire {myLock}:UUID1:ThreadID1:rwlock_timeout:2 30000

//执行结果
//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 2
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:2 ==> 1

(2)同一个客户端线程先加读锁再加写锁

客户端A(UUID1:ThreadID1)先加了一次读锁时：

//传入参数
KEYS[1] = myLock
KEYS[2] = {myLock}:UUID1:ThreadID1:rwlock_timeout 

ARGV[1] = 30000
ARGV[2] = UUID1:ThreadID1
ARGV[3] = UUID1:ThreadID1:write

//执行结果
//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 1
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1

客户端A(UUID1:ThreadID1)再加一次写锁时，判断不通过，不可以加成功。

//传入参数
KEYS[1] = myLock
ARGV[1] = 30000
ARGV[2] = UUID1:ThreadID1:write

执行命令"hget myLock mode"，发现mode = read，不符合加写锁条件。所以同一个客户端线程，先加读锁再加写锁，是会互斥的。

(3)同一个客户端线程先加写锁再加读锁

客户端A(UUID1:ThreadID1)先加了一次写锁时：

//传入参数
KEYS[1] = myLock
ARGV[1] = 30000
ARGV[2] = UUID1:ThreadID1:write

//执行结果
myLock: {
    "mode": "write",
    "UUID1:ThreadID1:write": 1
}

客户端A(UUID1:ThreadID1)再加一次读锁时，判断通过，可以加成功。

//传入参数
KEYS[1] = myLock
KEYS[2] = {myLock}:UUID1:ThreadID1:rwlock_timeout 
ARGV[1] = 30000
ARGV[2] = UUID1:ThreadID1
ARGV[3] = UUID1:ThreadID1:write

//执行命令
hget myLock mode，发现mode=write，表示已经加过写锁
hexists myLock UUID1:ThreadID1:write，判断写锁是自己加的，条件成立
hincrby myLock UUID1:ThreadID1 1，表示此时加了一个读锁
set {myLock}:UUID1:ThreadID1:rwlock_timeout:1 1
pexpire myLock 30000
pexpire {myLock}:UUID1:ThreadID11:rwlock_timeout:1 30000

//执行结果
//Hash结构
myLock: {
    "mode": "write",
    "UUID1:ThreadID1:write": 1,
    "UUID1:ThreadID1": 1
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1

可见：如果是同一个客户端线程，先加写锁再加读锁，是可以加成功的。所以默认在线程持有写锁的期间，同样的线程可以多次加读锁。

(4)同一个客户端线程先加写锁再加写锁

客户端A(UUID1:ThreadID1)先加了一次写锁时：

//传入参数
KEYS[1] = myLock
ARGV[1] = 30000
ARGV[2] = UUID1:ThreadID1:write

//执行结果
myLock: {
    "mode": "write",
    "UUID1:ThreadID1:write": 1
}

客户端A(UUID1:ThreadID1)再加一次写锁时，判断通过，可以加成功。

//执行命令
hexists myLock UUID1:ThreadID1:write，判断是否是自己加的写锁
hincrby myLock UUID1:ThreadID1:write 1
pexpire myLock 50000

//执行结果
myLock: {
    "mode": "write",
    "UUID1:ThreadID1:write": 2
}

可见：读写锁也是一种可重入锁。同一个客户端线程多次加写锁，是可以重入加锁的。先加的写锁是可以被读锁重入，先加的读锁则不可以被写锁重入。

8.读锁RedissonReadLock的释放读锁逻辑

(1)RedissonReadLock的释放读锁的流程

(2)释放读锁前主要三种情况

(3)RedissonReadLock的释放读锁的lua脚本

(4)对合并的情况一和情况二执行lua脚本

(5)对情况三执行lua脚本

(1)RedissonReadLock的释放读锁的流程

释放读锁调用的是RedissonLock的unlock()方法。

在RedissonLock的unlock()方法中，会执行get(unlockAsync())代码。也就是首先调用RedissonBaseLock的unlockAsync()方法，然后调用RedissonObject的get()方法。

其中unlockAsync()方法是异步化执行的方法，释放锁的操作就是异步执行的。而RedisObject的get()方法会通过RFuture同步等待获取异步执行的结果，可以将get(unlockAsync())理解为异步转同步。

在RedissonBaseLock的unlockAsync()方法中：可重入锁会调用RedissonLock.unlockInnerAsync()方法进行异步释放锁，读锁则会调用RedissonReadLock的unlockInnerAsync()方法进行异步释放锁，然后当完成释放锁的处理后，再通过异步去取消定时调度任务。

public class Application {
    public static void main(String[] args) throws Exception {
        Config config = new Config();
        config.useClusterServers().addNodeAddress("redis://192.168.1.110:7001");
        //读写锁
        RedissonClient redisson = Redisson.create(config);
        RReadWriteLock rwlock = redisson.getReadWriteLock("myLock");
        rwlock.readLock().lock();//获取读锁
        rwlock.readLock().unlock();//释放读锁
        rwlock.writeLock().lock();//获取写锁
        rwlock.writeLock().unlock();//释放写锁
        ...
    }
}

public class RedissonLock extends RedissonBaseLock {
    ...
    @Override
    public void unlock() {
        ...
        //异步转同步
        //首先调用的是RedissonBaseLock的unlockAsync()方法
        //然后调用的是RedissonObject的get()方法
        get(unlockAsync(Thread.currentThread().getId()));
        ...
    }
    ...
}

public abstract class RedissonBaseLock extends RedissonExpirable implements RLock {
    ...
    @Override
    public RFuture<Void> unlockAsync(long threadId) {
        //异步执行释放锁的lua脚本
        RFuture<Boolean> future = unlockInnerAsync(threadId);
        CompletionStage<Void> f = future.handle((opStatus, e) -> {
            //取消定时调度任务
            cancelExpirationRenewal(threadId);
            if (e != null) {
                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);
    }
    protected abstract RFuture<Boolean> unlockInnerAsync(long threadId);
    ...
}

public class RedissonReadLock extends RedissonLock implements RLock {
    ...
    @Override
    protected RFuture<Boolean> unlockInnerAsync(long threadId) {
        String timeoutPrefix = getReadWriteTimeoutNamePrefix(threadId);
        String keyPrefix = getKeyPrefix(threadId, timeoutPrefix);
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,
            "...",
            Arrays.<Object>asList(getRawName(), getChannelName(), timeoutPrefix, keyPrefix),
            LockPubSub.UNLOCK_MESSAGE,
            getLockName(threadId)
        );
    }
    ...
}

(2)释放读锁前主要三种情况

情况一：不同客户端线程加了读锁

//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 1,
    "UUID2:ThreadID2": 1,
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID2:ThreadID2:rwlock_timeout:1 ==> 1

情况二：同一个客户端线程多次重入加读锁

//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 2
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:2 ==> 1

情况一可以和情况二进行合并：

//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 2,
    "UUID2:ThreadID2": 1,
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:2 ==> 1
{myLock}:UUID2:ThreadID2:rwlock_timeout:1 ==> 1

情况三：同一个客户端线程先加写锁再加读锁

//Hash结构
myLock: {
    "mode": "write",
    "UUID1:ThreadID1:write": 1,
    "UUID1:ThreadID1": 1
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1

(3)RedissonReadLock的释放读锁的lua脚本

public class RedissonReadLock extends RedissonLock implements RLock {
    ...
    @Override
    protected RFuture<Boolean> unlockInnerAsync(long threadId) {
        String timeoutPrefix = getReadWriteTimeoutNamePrefix(threadId);
        String keyPrefix = getKeyPrefix(threadId, timeoutPrefix);
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,
            //执行命令"hget myLock mode"
            "local mode = redis.call('hget', KEYS[1], 'mode'); " +
            //如果mode为false就发布一个消息
            "if (mode == false) then " +
                "redis.call('publish', KEYS[2], ARGV[1]); " +
                "return 1; " +
            "end; " +
            //执行命令"hexists myLock UUID1:ThreadIdD1"，判断当前线程对应的Hash值是否存在
            "local lockExists = redis.call('hexists', KEYS[1], ARGV[2]); " +
            "if (lockExists == 0) then " +
                "return nil;" +
            "end; " +
            //执行命令"hincrby myLock UUID1:ThreadID1 -1"，递减当前线程对应的Hash值                
            "local counter = redis.call('hincrby', KEYS[1], ARGV[2], -1); " + 
            "if (counter == 0) then " +
                "redis.call('hdel', KEYS[1], ARGV[2]); " + 
            "end;" +
            //例如执行"del {myLock}:UUID1:ThreadId1:rwlock_timeout:2"
            //删除当前客户端线程UUID1:ThreadId1的一个重入读锁；
            "redis.call('del', KEYS[3] .. ':' .. (counter+1)); " +
            //执行命令"hlen myLock > 1"，判断Hash里的元素是否超过1个
            "if (redis.call('hlen', KEYS[1]) > 1) then " +
                "local maxRemainTime = -3; " + 
                //获取key为锁名的Hash值的所有key
                "local keys = redis.call('hkeys', KEYS[1]); " + 
                //遍历这些key，获取这些重入和非重入的读锁的最大剩余过期时间
                "for n, key in ipairs(keys) do " + 
                    "counter = tonumber(redis.call('hget', KEYS[1], key)); " + 
                    //把key为mode的kv对排除
                    "if type(counter) == 'number' then " + 
                        //通过递减拼接重入锁的key
                        "for i=counter, 1, -1 do " + 
                            "local remainTime = redis.call('pttl', KEYS[4] .. ':' .. key .. ':rwlock_timeout:' .. i); " + 
                            "maxRemainTime = math.max(remainTime, maxRemainTime);" + 
                        "end; " + 
                    "end; " + 
                "end; " +
                //找出所有重入的和非重入的读锁的最大剩余过期时间后，就重置锁的过期时间为该时间
                "if maxRemainTime > 0 then " +
                    "redis.call('pexpire', KEYS[1], maxRemainTime); " +
                    "return 0; " +
                "end;" + 
                    
                "if mode == 'write' then " + 
                    "return 0;" + 
                "end; " +
            "end; " +
            //删除锁
            "redis.call('del', KEYS[1]); " +
            //发布一个事件
            "redis.call('publish', KEYS[2], ARGV[1]); " +
            "return 1; ",
            //KEYS[1] = myLock，表示锁的名字
            //KEYS[2] = redisson_rwlock:{myLock}，用于Redis的发布订阅用
            //KEYS[3] = {myLock}:UUID1:ThreadID1:rwlock_timeout
            //KEYS[4] = {myLock}
            Arrays.<Object>asList(getRawName(), getChannelName(), timeoutPrefix, keyPrefix),
            LockPubSub.UNLOCK_MESSAGE,//ARGV[1] = 0，表示发布事件类型
            getLockName(threadId)//ARGV[2] = UUID1:ThreadID1，表示锁里面的该客户端线程代表的key
        );
    }
    ...
}

参数说明：

KEYS[1] = myLock，表示锁的名字
KEYS[2] = redisson_rwlock:{myLock}，用于Redis的发布订阅用
KEYS[3] = {myLock}:UUID1:ThreadID1:rwlock_timeout
KEYS[4] = {myLock}
ARGV[1] = 0，表示发布事件类型
ARGV[2] = UUID1:ThreadID1，表示锁里面的该客户端线程代表的key

(4)对合并的情况一和情况二执行lua脚本

一.客户端A(UUID1:ThreadID1)先释放一次读锁

二.客户端A(UUID1:ThreadID1)再释放一次读锁

三.客户端B(UUID2:ThreadID2)再释放一次读锁

//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 2,
    "UUID2:ThreadID2": 1,
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID1:ThreadID1:rwlock_timeout:2 ==> 1
{myLock}:UUID2:ThreadID2:rwlock_timeout:1 ==> 1

一.客户端A(UUID1:ThreadID1)先释放一次读锁

首先执行命令"hget myLock mode"，发现mode = read。然后执行命令"hexists myLock UUID1:ThreadIdD1"，发现肯定是存在的，因为这个客户端线程UUID1:ThreadIdD1加过读锁。

接着执行命令"hincrby myLock UUID1:ThreadID1 -1"，将这个客户端线程对应的加读锁次数递减1，counter由2变成1。当counter大于1，说明还有线程持有着这个读锁。于是接着执行"del {myLock}:UUID1:ThreadId1:rwlock_timeout:2"，也就是删除用来记录当前客户端线程第2个重入锁过期时间的key。

此时myLock锁的数据变成如下：

//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 1,
    "UUID2:ThreadID2": 1,
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1
{myLock}:UUID2:ThreadID2:rwlock_timeout:1 ==> 1

于是接着执行命令"hlen myLock"，判断Hash里的元素是否超过1个。如果超过1，那么就遍历已被线程获取的所有重入和非重入的读锁，即遍历所有类似"{myLock}:UUID2:ThreadID2:rwlock_timeout:1"的key。

然后接着执行命令"pttl {myLock}:UUID1:ThreadID1:rwlock_timeout:1"。即获取每一个重入读锁和非重入读锁的剩余过期时间，并找出其中最大的。执行"pexpire myLock"重置读锁的过期时间，为最大的剩余过期时间。

二.客户端A(UUID1:ThreadID1)再释放一次读锁

首先执行命令"hincrby myLock UUID1:ThreadID1 -1"，将这个客户端线程对应的加读锁次数递减1，counter由1变成0。当counter=0时，就执行命令"hdel myLock UUID1:ThreadID1"，即删除用来记录当前客户端线程重入锁次数的key。

然后接着执行命令"del {myLock}:UUID1:ThreadID1:rwlock_timeout:1"，即删除用来记录当前客户端线程第1个重入锁过期时间的key。最后获取每个重入读锁和非重入读锁的剩余过期时间，并找出其中最大的。执行"pexpire myLock"重置读锁的过期时间，为最大的剩余过期时间。

此时myLock锁的数据变成如下：

//Hash结构
myLock: {
    "mode": "read",
    "UUID2:ThreadID2": 1,
}
//String结构
{myLock}:UUID2:ThreadID2:rwlock_timeout:1 ==> 1

三.客户端B(UUID2:ThreadID2)再释放一次读锁

首先执行命令"hincrby myLock UUID2:ThreadID2 -1"，将这个客户端线程对应的加读锁次数递减1，counter由1变成0。然后执行命令"hdel myLock UUID2:ThreadID2"，即删除用来记录当前客户端线程重入锁次数的key。接着执行命令"del {myLock}:UUID1:ThreadID1:rwlock_timeout:1"，即删除用来记录当前客户端线程第1个重入锁过期时间的key。

此时myLock锁的数据变成如下：

//Hash结构
myLock: {
    "mode": "read"
}

此时继续执行命令"hlen myLock"，发现为1，判断不通过，于是执行"del myLock"。也就是当没有线程再持有这个读锁时，就会彻底删除这个读锁，然后发布一个事件出去。

(5)对情况三执行lua脚本

这种情况是：同一个客户端线程先加写锁再加读锁。此时myLock锁的数据如下：

//Hash结构
myLock: {
    "mode": "write",
    "UUID1:ThreadID1:write": 1,
    "UUID1:ThreadID1": 1
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1

首先执行命令"hincrby myLock UUID1:ThreadID1 -1"，将这个客户端线程对应的加读锁次数递减1，counter由1变成0。然后执行命令"hdel myLock UUID1:ThreadID1"，即删除用来记录当前客户端线程重入锁次数的key。接着执行"del {myLock}:UUID1:ThreadID1:rwlock_timeout:1"，即删除用来记录当前客户端线程第1个重入锁过期时间的key。

此时myLock锁的数据变成如下：

//Hash结构
myLock: {
    "mode": "write",
    "UUID1:ThreadID1:write": 1
}

接着执行命令"hlen myLock > 1"，判断Hash里的元素是否超过1个。发现判断通过，但由于没有了读锁，所以最后会判断mode如果是write，就返回0。

9.写锁RedissonWriteLock的释放写锁逻辑

(1)释放写锁前主要有两种情况

(2)RedissonWriteLock的释放写锁的lua脚本

(3)执行释放写锁的lua脚本

(1)释放写锁前主要有两种情况

情况一：同一个客户端线程多次重入加写锁

情况二：同一个客户端线程先加写锁再加读锁

这两种情况的锁数据可以合并为如下：

//Hash结构
myLock: {
    "mode": "write",
    "UUID1:ThreadID1:write": 2,
    "UUID1:ThreadID1": 1
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1

接下来以这种锁数据为前提进行lua脚本分析。

(2)RedissonWriteLock的释放写锁的lua脚本

public class RedissonWriteLock extends RedissonLock implements RLock {
    ...
    @Override
    protected RFuture<Boolean> unlockInnerAsync(long threadId) {
        return evalWriteAsync(getRawName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,
            //首先执行命令"hget myLock mode"，发现mode=write
            "local mode = redis.call('hget', KEYS[1], 'mode'); " +
            "if (mode == false) then " +
                "redis.call('publish', KEYS[2], ARGV[1]); " +
                "return 1; " +
            "end;" +
            "if (mode == 'write') then " +
                //然后执行命令"hexists myLock UUID1:ThreadIdD1:write"，发现存在
                "local lockExists = redis.call('hexists', KEYS[1], ARGV[3]); " +
                "if (lockExists == 0) then " +
                    "return nil;" +
                "else " +
                    //于是接着执行命令"hincrby myLock UUID1:ThreadID1:write -1"
                    "local counter = redis.call('hincrby', KEYS[1], ARGV[3], -1); " +
                    "if (counter > 0) then " +
                        //当counter大于0，说明还有线程持有写锁，那么就重置锁的过期时间
                        "redis.call('pexpire', KEYS[1], ARGV[2]); " +
                        "return 0; " +
                    "else " +
                        //当counter为0，就执行命令"hdel myLock UUID1:ThreadID1:write"
                        "redis.call('hdel', KEYS[1], ARGV[3]); " +
                        //判断key为锁名的Hash里元素是否超过1个
                        "if (redis.call('hlen', KEYS[1]) == 1) then " +
                            //如果只有1个，则说明没有线程持有锁了，此时可以删除掉锁对应的key
                            "redis.call('del', KEYS[1]); " +
                            "redis.call('publish', KEYS[2], ARGV[1]); " + 
                        "else " +
                            //如果有超过1个，则说明还有线程持有读锁，此时需要将写锁转读锁
                            "redis.call('hset', KEYS[1], 'mode', 'read'); " +
                        "end; " +
                        "return 1; "+
                    "end; " +
                "end; " +
            "end; " +
            "return nil;",
            //KEYS[1] = myLock，KEYS[2] = redisson_rwlock:{myLock}
            Arrays.<Object>asList(getRawName(), getChannelName()),
            LockPubSub.READ_UNLOCK_MESSAGE,//ARGV[1] = 0
            internalLockLeaseTime,//ARGV[2] = 30000
            getLockName(threadId)//ARGV[3] = UUID1:ThreadID1:write
        );
    }
    ...
}

(3)执行释放写锁的lua脚本

一.参数说明

KEYS[1] = myLock
KEYS[2] = redisson_rwlock:{myLock}
ARGV[1] = 0
ARGV[2] = 30000
ARGV[3] = UUID1:ThreadID1:write

二.lua脚本执行分析

首先执行命令"hget myLock mode"，发现mode = write。然后执行命令"hexists myLock UUID1:ThreadIdD1:write"，发现存在。于是接着执行命令"hincrby myLock UUID1:ThreadID1:write -1"，也就是将这个客户端线程对应的加写锁次数递减1，counter由2变成1。当counter大于0，说明还有线程持有写锁，那么就重置锁的过期时间。当counter为0，就执行命令"hdel myLock UUID1:ThreadID1:write"，即删除用来记录当前客户端线程重入写锁次数的key。

删除后，myLock的锁数据如下：

//Hash结构
myLock: {
    "mode": "write",
    "UUID1:ThreadID1": 1
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1

接着执行命令"hlen myLock"，判断key为锁名的Hash里元素是否超过1个。如果只有1个，则说明没有线程持有锁了，此时可以删除掉锁对应的key。如果有超过1个，则说明还有线程持有读锁，此时需要将写锁转读锁。

因此，最后myLock的锁数据如下：

//Hash结构
myLock: {
    "mode": "read",
    "UUID1:ThreadID1": 1
}
//String结构
{myLock}:UUID1:ThreadID1:rwlock_timeout:1 ==> 1