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 ==> 13.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:writeRedis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 30000Redis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:writeRedis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 30000Redis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。