大纲

1.Redisson可重入锁RedissonLock概述

2.可重入锁源码之创建RedissonClient实例

3.可重入锁源码之lua脚本加锁逻辑

4.可重入锁源码之WatchDog维持加锁逻辑

5.可重入锁源码之可重入加锁逻辑

6.可重入锁源码之锁的互斥阻塞逻辑

7.可重入锁源码之释放锁逻辑

8.可重入锁源码之获取锁超时与锁超时自动释放逻辑

9.可重入锁源码总结

1.Redisson可重入锁RedissonLock概述

(1)在pom.xml里引入依赖

(2)构建RedissonClient并使用Redisson

(3)Redisson可重入锁RedissonLock简单使用

(1)在pom.xml里引入依赖

<dependencies><dependency><groupId>org.redisson</groupId><artifactId>redisson</artifactId><version>3.16.8</version></dependency> 
</dependencies>

(2)构建RedissonClient并使用Redisson

参考官网中文文档，连接上3主3从的Redis Cluster。

//https://github.com/redisson/redisson/wiki/目录
public class Application {public static void main(String[] args) throws Exception {//连接3主3从的Redis CLusterConfig config = new Config();config.useClusterServers().addNodeAddress("redis://192.168.1.110:7001").addNodeAddress("redis://192.168.1.110:7002").addNodeAddress("redis://192.168.1.110:7003").addNodeAddress("redis://192.168.1.111:7001").addNodeAddress("redis://192.168.1.111:7002").addNodeAddress("redis://192.168.1.111:7003");//创建RedissonClient实例RedissonClient redisson = Redisson.create(config);//获取可重入锁RLock lock = redisson.getLock("myLock");lock.lock();lock.unlock();RMap<String, Object> map = redisson.getMap("myMap");map.put("foo", "bar");  map = redisson.getMap("myMap");System.out.println(map.get("foo"));   }
}

(3)Redisson可重入锁RedissonLock简单使用

Redisson可重入锁RLock实现了java.util.concurrent.locks.Lock接口，同时还提供了异步(Async)、响应式(Reactive)和RxJava2标准的接口。

RLock lock = redisson.getLock("myLock");
//最常见的使用方法
lock.lock();

如果设置锁的超时时间不合理，导致超时时间已到时锁还没能主动释放，但实际上锁却被Redis节点通过过期时间释放了，这会有问题。

为了避免这种情况，Redisson内部提供了一个用来监控锁的WatchDog。WatchDog的作用是在Redisson实例被关闭前，不断地延长锁的有效期。

WatchDog检查锁的默认超时时间是30秒，可通过Config.lockWatchdogTimeout来指定。

RLock的tryLock方法提供了leaseTime参数来指定加锁的超时时间，超过这个时间后锁便自动被释放。

//如果没有主动释放锁的话，10秒后将会自动释放锁
lock.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 = lock.tryLock(100, 10, TimeUnit.SECONDS);
if (res) {try {...} finally {lock.unlock();}
}

RLock完全符合Java的Lock规范，即只有拥有锁的进程才能解锁，其他进程解锁则会抛出IllegalMonitorStateException错误。如果需要其他进程也能解锁，那么可以使用分布式信号量Semaphore。

2.可重入锁源码之创建RedissonClient实例

(1)初始化与Redis的连接管理器ConnectionManager

(2)初始化Redis的命令执行器CommandExecutor

使用Redisson.create()方法可以根据配置创建一个RedissonClient实例，因为Redisson类会实现RedissonClient接口，而创建RedissonClient实例的主要工作其实就是：

一.初始化与Redis的连接管理器ConnectionManager

二.初始化Redis的命令执行器CommandExecutor

(1)初始化与Redis的连接管理器ConnectionManager

Redis的配置类Config会被封装在连接管理器ConnectionManager中，后续可以通过连接管理器ConnectionManager获取Redis的配置类Config。

public class Application {public static void main(String[] args) throws Exception {Config config = new Config();config.useClusterServers().addNodeAddress("redis://192.168.1.110:7001");//创建RedissonClient实例RedissonClient redisson = Redisson.create(config);...}
}//创建RedissonClient实例的源码
public class Redisson implements RedissonClient {protected final Config config;//Redis配置类protected final ConnectionManager connectionManager;//Redis的连接管理器protected final CommandAsyncExecutor commandExecutor;//Redis的命令执行器...public static RedissonClient create(Config config) {return new Redisson(config);}protected Redisson(Config config) {this.config = config;Config configCopy = new Config(config);//根据Redis配置类Config实例创建和Redis的连接管理器connectionManager = ConfigSupport.createConnectionManager(configCopy);RedissonObjectBuilder objectBuilder = null;if (config.isReferenceEnabled()) {objectBuilder = new RedissonObjectBuilder(this);}//创建Redis的命令执行器commandExecutor = new CommandSyncService(connectionManager, objectBuilder);evictionScheduler = new EvictionScheduler(commandExecutor);writeBehindService = new WriteBehindService(commandExecutor);}...
}public class ConfigSupport {...//创建Redis的连接管理器public static ConnectionManager createConnectionManager(Config configCopy) {//生成UUIDUUID id = UUID.randomUUID();...if (configCopy.getClusterServersConfig() != null) {validate(configCopy.getClusterServersConfig());//返回ClusterConnectionManager实例return new ClusterConnectionManager(configCopy.getClusterServersConfig(), configCopy, id);}...}...
}public class ClusterConnectionManager extends MasterSlaveConnectionManager {public ClusterConnectionManager(ClusterServersConfig cfg, Config config, UUID id) {super(config, id);...this.natMapper = cfg.getNatMapper();//将Redis的配置类Config封装在ConnectionManager中this.config = create(cfg);initTimer(this.config);Throwable lastException = null;List<String> failedMasters = new ArrayList<String>();for (String address : cfg.getNodeAddresses()) {RedisURI addr = new RedisURI(address);//异步连接Redis节点CompletionStage<RedisConnection> connectionFuture = connectToNode(cfg, addr, addr.getHost());...//通过connectionFuture阻塞获取建立好的连接RedisConnection connection = connectionFuture.toCompletableFuture().join();...List<ClusterNodeInfo> nodes = connection.sync(clusterNodesCommand);...CompletableFuture<Collection<ClusterPartition>> partitionsFuture = parsePartitions(nodes);Collection<ClusterPartition> partitions = partitionsFuture.join();List<CompletableFuture<Void>> masterFutures = new ArrayList<>();for (ClusterPartition partition : partitions) {if (partition.isMasterFail()) {failedMasters.add(partition.getMasterAddress().toString());continue;}if (partition.getMasterAddress() == null) {throw new IllegalStateException("Master node: " + partition.getNodeId() + " doesn't have address.");}CompletableFuture<Void> masterFuture = addMasterEntry(partition, cfg);masterFutures.add(masterFuture);}CompletableFuture<Void> masterFuture = CompletableFuture.allOf(masterFutures.toArray(new CompletableFuture[0]));masterFuture.join();...}...}...
}public class MasterSlaveConnectionManager implements ConnectionManager {protected final String id;//初始化时为UUIDprivate final Map<RedisURI, RedisConnection> nodeConnections = new ConcurrentHashMap<>();...protected MasterSlaveConnectionManager(Config cfg, UUID id) {this.id = id.toString();//传入的是UUIDthis.cfg = cfg;...}protected final CompletionStage<RedisConnection> connectToNode(NodeType type, BaseConfig<?> cfg, RedisURI addr, String sslHostname) {RedisConnection conn = nodeConnections.get(addr);if (conn != null) {if (!conn.isActive()) {closeNodeConnection(conn);} else {return CompletableFuture.completedFuture(conn);}}//创建Redis客户端连接实例RedisClient client = createClient(type, addr, cfg.getConnectTimeout(), cfg.getTimeout(), sslHostname);//向Redis服务端发起异步连接请求，这个future会层层往外返回CompletionStage<RedisConnection> future = client.connectAsync();return future.thenCompose(connection -> {if (connection.isActive()) {if (!addr.isIP()) {RedisURI address = new RedisURI(addr.getScheme() + "://" + connection.getRedisClient().getAddr().getAddress().getHostAddress() + ":" + connection.getRedisClient().getAddr().getPort());nodeConnections.put(address, connection);}nodeConnections.put(addr, connection);return CompletableFuture.completedFuture(connection);} else {connection.closeAsync();CompletableFuture<RedisConnection> f = new CompletableFuture<>();f.completeExceptionally(new RedisException("Connection to " + connection.getRedisClient().getAddr() + " is not active!"));return f;}});}//创建Redis客户端连接实例@Overridepublic RedisClient createClient(NodeType type, RedisURI address, int timeout, int commandTimeout, String sslHostname) {RedisClientConfig redisConfig = createRedisConfig(type, address, timeout, commandTimeout, sslHostname);return RedisClient.create(redisConfig);}...
}//Redisson主要使用Netty去和Redis服务端建立连接
public final class RedisClient {private final Bootstrap bootstrap;private final Bootstrap pubSubBootstrap;...public static RedisClient create(RedisClientConfig config) {return new RedisClient(config);}private RedisClient(RedisClientConfig config) {...bootstrap = createBootstrap(copy, Type.PLAIN);pubSubBootstrap = createBootstrap(copy, Type.PUBSUB);this.commandTimeout = copy.getCommandTimeout();}private Bootstrap createBootstrap(RedisClientConfig config, Type type) {Bootstrap bootstrap = new Bootstrap().resolver(config.getResolverGroup()).channel(config.getSocketChannelClass()).group(config.getGroup());bootstrap.handler(new RedisChannelInitializer(bootstrap, config, this, channels, type));bootstrap.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, config.getConnectTimeout());bootstrap.option(ChannelOption.SO_KEEPALIVE, config.isKeepAlive());bootstrap.option(ChannelOption.TCP_NODELAY, config.isTcpNoDelay());config.getNettyHook().afterBoostrapInitialization(bootstrap);return bootstrap;}//向Redis服务端发起异步连接请求public RFuture<RedisConnection> connectAsync() {CompletableFuture<InetSocketAddress> addrFuture = resolveAddr();CompletableFuture<RedisConnection> f = addrFuture.thenCompose(res -> {CompletableFuture<RedisConnection> r = new CompletableFuture<>();//Netty的Bootstrap发起连接ChannelFuture channelFuture = bootstrap.connect(res);channelFuture.addListener(new ChannelFutureListener() {@Overridepublic void operationComplete(final ChannelFuture future) throws Exception {if (bootstrap.config().group().isShuttingDown()) {IllegalStateException cause = new IllegalStateException("RedisClient is shutdown");r.completeExceptionally(cause);return;}if (future.isSuccess()) {RedisConnection c = RedisConnection.getFrom(future.channel());c.getConnectionPromise().whenComplete((res, e) -> {bootstrap.config().group().execute(new Runnable() {@Overridepublic void run() {if (e == null) {if (!r.complete(c)) {c.closeAsync();}} else {r.completeExceptionally(e);c.closeAsync();}}});});} else {bootstrap.config().group().execute(new Runnable() {public void run() {r.completeExceptionally(future.cause());}});}}});return r;});return new CompletableFutureWrapper<>(f);}...
}

(2)初始化Redis的命令执行器CommandExecutor

首先，CommandSyncService继承自CommandAsyncService类。

而CommandAsyncService类实现了CommandExecutor接口。

然后，ConnectionManager连接管理器会封装在命令执行器CommandExecutor中。

所以，通过CommandExecutor命令执行器可以获取连接管理器ConnectionManager。

//Redis命令的同步执行器CommandSyncService
public class CommandSyncService extends CommandAsyncService implements CommandExecutor {//初始化CommandExecutorpublic CommandSyncService(ConnectionManager connectionManager, RedissonObjectBuilder objectBuilder) {super(connectionManager, objectBuilder, RedissonObjectBuilder.ReferenceType.DEFAULT);}public <T, R> R read(String key, RedisCommand<T> command, Object... params) {return read(key, connectionManager.getCodec(), command, params);}public <T, R> R read(String key, Codec codec, RedisCommand<T> command, Object... params) {RFuture<R> res = readAsync(key, codec, command, params);return get(res);}public <T, R> R evalRead(String key, RedisCommand<T> evalCommandType, String script, List<Object> keys, Object... params) {return evalRead(key, connectionManager.getCodec(), evalCommandType, script, keys, params);}public <T, R> R evalRead(String key, Codec codec, RedisCommand<T> evalCommandType, String script, List<Object> keys, Object... params) {RFuture<R> res = evalReadAsync(key, codec, evalCommandType, script, keys, params);return get(res);}public <T, R> R evalWrite(String key, RedisCommand<T> evalCommandType, String script, List<Object> keys, Object... params) {return evalWrite(key, connectionManager.getCodec(), evalCommandType, script, keys, params);}public <T, R> R evalWrite(String key, Codec codec, RedisCommand<T> evalCommandType, String script, List<Object> keys, Object... params) {RFuture<R> res = evalWriteAsync(key, codec, evalCommandType, script, keys, params);return get(res);}
}//Redis命令的异步执行器CommandAsyncService
public class CommandAsyncService implements CommandAsyncExecutor {//Redis连接管理器final ConnectionManager connectionManager;final RedissonObjectBuilder objectBuilder;final RedissonObjectBuilder.ReferenceType referenceType;public CommandAsyncService(ConnectionManager connectionManager, RedissonObjectBuilder objectBuilder, RedissonObjectBuilder.ReferenceType referenceType) {this.connectionManager = connectionManager;this.objectBuilder = objectBuilder;this.referenceType = referenceType;}@Overridepublic <V> V getNow(CompletableFuture<V> future) {try {return future.getNow(null);} catch (Exception e) {return null;}}@Overridepublic <T, R> R read(String key, Codec codec, RedisCommand<T> command, Object... params) {RFuture<R> res = readAsync(key, codec, command, params);return get(res);}@Overridepublic <T, R> RFuture<R> readAsync(String key, Codec codec, RedisCommand<T> command, Object... params) {NodeSource source = getNodeSource(key);return async(true, source, codec, command, params, false, false);}private NodeSource getNodeSource(String key) {int slot = connectionManager.calcSlot(key);return new NodeSource(slot);}public <V, R> RFuture<R> async(boolean readOnlyMode, NodeSource source, Codec codec, RedisCommand<V> command, Object[] params, boolean ignoreRedirect, boolean noRetry) {CompletableFuture<R> mainPromise = createPromise();RedisExecutor<V, R> executor = new RedisExecutor<>(readOnlyMode, source, codec, command, params, mainPromise, ignoreRedirect, connectionManager, objectBuilder, referenceType, noRetry);executor.execute();return new CompletableFutureWrapper<>(mainPromise);}@Overridepublic <V> V get(RFuture<V> future) {if (Thread.currentThread().getName().startsWith("redisson-netty")) {throw new IllegalStateException("Sync methods can't be invoked from async/rx/reactive listeners");}try {return future.toCompletableFuture().get();} catch (InterruptedException e) {future.cancel(true);Thread.currentThread().interrupt();throw new RedisException(e);} catch (ExecutionException e) {throw convertException(e);}}...
}

3.可重入锁源码之lua脚本加锁逻辑

(1)通过Redisson.getLock()方法获取一个RedissonLock实例

(2)加锁时的执行流程

(3)加锁时执行的lua脚本

(4)执行加锁lua脚本的命令执行器逻辑

(5)如何根据slot值获取对应的节点

(1)通过Redisson.getLock()方法获取一个RedissonLock实例

在Redisson.getLock()方法中，会传入命令执行器CommandExecutor来创建一个RedissonLock实例，而命令执行器CommandExecutor是在执行Redisson.create()方法时初始化好的，所以命令执行器CommandExecutor会被封装在RedissonLock实例中。

因此，通过RedissonLock实例可以获取一个命令执行器CommandExecutor，通过命令执行器CommandExecutor可获取连接管理器ConnectionManager，通过连接管理器ConnectionManager可获取Redis的配置信息类Config，通过Redis的配置信息类Config可以获取各种配置信息。

RedissonLock类继承自实现了RLock接口的RedissonBaseLock类。在RedissonLock的构造方法里面，有个internalLockLeaseTime变量，这个internalLockLeaseTime变量与WatchDog看门狗有关系。interlnalLockLeaseTime的默认值是30000毫秒，即30秒；

public class Application {public static void main(String[] args) throws Exception {Config config = new Config();config.useClusterServers().addNodeAddress("redis://192.168.1.110:7001");//创建RedissonClient实例RedissonClient redisson = Redisson.create(config);//获取可重入锁RLock lock = redisson.getLock("myLock");lock.lock();...}
}//创建Redisson实例
public class Redisson implements RedissonClient {protected final Config config;//Redis配置类protected final ConnectionManager connectionManager;//Redis的连接管理器protected final CommandAsyncExecutor commandExecutor;//Redis的命令执行器...public static RedissonClient create(Config config) {return new Redisson(config);}protected Redisson(Config config) {...//根据Redis配置类Config实例创建和Redis的连接管理器connectionManager = ConfigSupport.createConnectionManager(configCopy);//创建Redis的命令执行器commandExecutor = new CommandSyncService(connectionManager, objectBuilder);...}...@Overridepublic RLock getLock(String name) {return new RedissonLock(commandExecutor, name);}...
}//创建RedissonLock实例
//通过RedissonLock实例可以获取一个命令执行器CommandExecutor；
public class RedissonLock extends RedissonBaseLock {protected long internalLockLeaseTime;protected final LockPubSub pubSub;final CommandAsyncExecutor commandExecutor;public RedissonLock(CommandAsyncExecutor commandExecutor, String name) {super(commandExecutor, name);this.commandExecutor = commandExecutor;//与WatchDog有关的internalLockLeaseTime//通过命令执行器CommandExecutor可以获取连接管理器ConnectionManager//通过连接管理器ConnectionManager可以获取Redis的配置信息类Config//通过Redis的配置信息类Config可以获取lockWatchdogTimeout超时时间this.internalLockLeaseTime = commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout();this.pubSub = commandExecutor.getConnectionManager().getSubscribeService().getLockPubSub();}...
}//创建Redis的命令执行器
//通过命令执行器CommandExecutor可以获取连接管理器ConnectionManager
public class CommandAsyncService implements CommandAsyncExecutor {final ConnectionManager connectionManager;...public CommandAsyncService(ConnectionManager connectionManager, RedissonObjectBuilder objectBuilder, RedissonObjectBuilder.ReferenceType referenceType) {this.connectionManager = connectionManager;this.objectBuilder = objectBuilder;this.referenceType = referenceType;}@Overridepublic ConnectionManager getConnectionManager() {return connectionManager;}...
}//创建Redis的连接管理器
//通过连接管理器ConnectionManager可以获取Redis的配置信息类Config
public class ClusterConnectionManager extends MasterSlaveConnectionManager {...public ClusterConnectionManager(ClusterServersConfig cfg, Config config, UUID id) {super(config, id);...}...
}//创建Redis的连接管理器
//通过连接管理器ConnectionManager可以获取Redis的配置信息类Config
public class MasterSlaveConnectionManager implements ConnectionManager {private final Config cfg;protected final String id;//初始化时为UUID...protected MasterSlaveConnectionManager(Config cfg, UUID id) {this.id = id.toString();//传入的是UUIDthis.cfg = cfg;...}@Overridepublic Config getCfg() {return cfg;}...
}//配置信息类Config中的lockWatchdogTimeout变量初始化为30秒，该变量与WatchDog有关
public class Config {private long lockWatchdogTimeout = 30 * 1000;...//This parameter is only used if lock has been acquired without leaseTimeout parameter definition. //Lock expires after "lockWatchdogTimeout" if watchdog didn't extend it to next "lockWatchdogTimeout" time interval.//This prevents against infinity locked locks due to Redisson client crush or any other reason when lock can't be released in proper way.//Default is 30000 millisecondspublic Config setLockWatchdogTimeout(long lockWatchdogTimeout) {this.lockWatchdogTimeout = lockWatchdogTimeout;return this;}public long getLockWatchdogTimeout() {return lockWatchdogTimeout;}
}

默认情况下，调用RedissonLock.lock()方法加锁时，传入的leaseTime为-1。此时锁的超时时间会设为lockWatchdogTimeout默认的30秒，从而避免出现死锁的情况。

public class RedissonLock extends RedissonBaseLock {...//加锁@Overridepublic void lock() {try {lock(-1, null, false);} catch (InterruptedException e) {throw new IllegalStateException();}}private void lock(long leaseTime, TimeUnit unit, boolean interruptibly) throws InterruptedException {long threadId = Thread.currentThread().getId();Long ttl = tryAcquire(-1, leaseTime, unit, threadId);...}//解锁@Overridepublic void unlock() {try {get(unlockAsync(Thread.currentThread().getId()));} catch (RedisException e) {if (e.getCause() instanceof IllegalMonitorStateException) {throw (IllegalMonitorStateException) e.getCause();} else {throw e;}}}...
}

(2)加锁时的执行流程

首先会调用RedissonLock的tryAcquire()方法处理异步RFuture相关，然后调用RedissonLock的tryAcquireAsync()方法对执行脚本的结果进行处理，接着调用RedissonLock.tryLockInnerAsync方法执行加锁的lua脚本。

public class RedissonLock extends RedissonBaseLock {protected long internalLockLeaseTime;protected final LockPubSub pubSub;final CommandAsyncExecutor commandExecutor;public RedissonLock(CommandAsyncExecutor commandExecutor, String name) {super(commandExecutor, name);this.commandExecutor = commandExecutor;//与WatchDog有关的internalLockLeaseTime//通过命令执行器CommandExecutor可以获取连接管理器ConnectionManager//通过连接管理器ConnectionManager可以获取Redis的配置信息类Config//通过Redis的配置信息类Config可以获取lockWatchdogTimeout超时时间this.internalLockLeaseTime = commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout();this.pubSub = commandExecutor.getConnectionManager().getSubscribeService().getLockPubSub();}...//加锁@Overridepublic void lock() {try {lock(-1, null, false);} catch (InterruptedException e) {throw new IllegalStateException();}}private void lock(long leaseTime, TimeUnit unit, boolean interruptibly) throws InterruptedException {//线程ID，用来生成设置Hash的值long threadId = Thread.currentThread().getId();//尝试加锁，此时执行RedissonLock.lock()方法默认传入的leaseTime=-1Long ttl = tryAcquire(-1, leaseTime, unit, threadId);//ttl为null说明加锁成功if (ttl == null) {return;}//加锁失败时的处理CompletableFuture<RedissonLockEntry> future = subscribe(threadId);if (interruptibly) {commandExecutor.syncSubscriptionInterrupted(future);} else {commandExecutor.syncSubscription(future);}try {while (true) {ttl = tryAcquire(-1, leaseTime, unit, threadId);// lock acquiredif (ttl == null) {break;}// waiting for messageif (ttl >= 0) {try {commandExecutor.getNow(future).getLatch().tryAcquire(ttl, TimeUnit.MILLISECONDS);} catch (InterruptedException e) {if (interruptibly) {throw e;}commandExecutor.getNow(future).getLatch().tryAcquire(ttl, TimeUnit.MILLISECONDS);}} else {if (interruptibly) {commandExecutor.getNow(future).getLatch().acquire();} else {commandExecutor.getNow(future).getLatch().acquireUninterruptibly();}}}} finally {unsubscribe(commandExecutor.getNow(future), threadId);}}...private Long tryAcquire(long waitTime, long leaseTime, TimeUnit unit, long threadId) {//默认下waitTime和leaseTime都是-1，下面调用的get方法是来自于RedissonObject的get()方法//可以理解为异步转同步：将异步的tryAcquireAsync通过get转同步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 {//默认情况下，由于leaseTime=-1，所以会使用初始化RedissonLock实例时的internalLockLeaseTime//internalLockLeaseTime的默认值就是lockWatchdogTimeout的默认值，30秒ttlRemainingFuture = tryLockInnerAsync(waitTime, internalLockLeaseTime, TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);}CompletionStage<Long> f = ttlRemainingFuture.thenApply(ttlRemaining -> {//加锁返回的ttlRemaining为null表示加锁成功if (ttlRemaining == null) {if (leaseTime != -1) {internalLockLeaseTime = unit.toMillis(leaseTime);} else {scheduleExpirationRenewal(threadId);}}return ttlRemaining;});return new CompletableFutureWrapper<>(f);}//默认情况下，外部传入的leaseTime=-1时，会取lockWatchdogTimeout的默认值=30秒<T> RFuture<T> tryLockInnerAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {return evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,"if (redis.call('exists', KEYS[1]) == 0) then " +"redis.call('hincrby', KEYS[1], ARGV[2], 1); " +"redis.call('pexpire', KEYS[1], ARGV[1]); " +"return nil; " +"end; " +"if (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; " +"return redis.call('pttl', KEYS[1]);",Collections.singletonList(getRawName()),//锁的名字：KEYS[1]unit.toMillis(leaseTime),//过期时间：ARGV[1]，默认时为30秒getLockName(threadId)//ARGV[2]，值为UUID + 线程ID);}...
}public abstract class RedissonBaseLock extends RedissonExpirable implements RLock {final String id;final String entryName;final CommandAsyncExecutor commandExecutor;public RedissonBaseLock(CommandAsyncExecutor commandExecutor, String name) {super(commandExecutor, name);this.commandExecutor = commandExecutor;this.id = commandExecutor.getConnectionManager().getId();this.internalLockLeaseTime = commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout();this.entryName = id + ":" + name;}protected String getLockName(long threadId) {return id + ":" + threadId;}...
}abstract class RedissonExpirable extends RedissonObject implements RExpirable {...RedissonExpirable(CommandAsyncExecutor connectionManager, String name) {super(connectionManager, name);}...
}public abstract class RedissonObject implements RObject {protected final CommandAsyncExecutor commandExecutor;protected String name;protected final Codec codec;public RedissonObject(Codec codec, CommandAsyncExecutor commandExecutor, String name) {this.codec = codec;this.commandExecutor = commandExecutor;if (name == null) {throw new NullPointerException("name can't be null");}setName(name);}...protected final <V> V get(RFuture<V> future) {//下面会调用CommandAsyncService.get()方法return commandExecutor.get(future);}...
}public class CommandAsyncService implements CommandAsyncExecutor {...@Overridepublic <V> V get(RFuture<V> future) {if (Thread.currentThread().getName().startsWith("redisson-netty")) {throw new IllegalStateException("Sync methods can't be invoked from async/rx/reactive listeners");}try {return future.toCompletableFuture().get();} catch (InterruptedException e) {future.cancel(true);Thread.currentThread().interrupt();throw new RedisException(e);} catch (ExecutionException e) {throw convertException(e);}}...
}

(3)加锁时执行的lua脚本

public class RedissonLock extends RedissonBaseLock {//默认情况下，外部传入的leaseTime=-1时，会取lockWatchdogTimeout的默认值=30秒<T> RFuture<T> tryLockInnerAsync(long waitTime, long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {return evalWriteAsync(getRawName(), LongCodec.INSTANCE, command,"if (redis.call('exists', KEYS[1]) == 0) then " +"redis.call('hincrby', KEYS[1], ARGV[2], 1); " +"redis.call('pexpire', KEYS[1], ARGV[1]); " +"return nil; " +"end; " +"if (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; " +"return redis.call('pttl', KEYS[1]);",Collections.singletonList(getRawName()),//锁的名字：KEYS[1]，比如"myLock"unit.toMillis(leaseTime),//过期时间：ARGV[1]，默认时为30秒getLockName(threadId)//ARGV[2]，值为UUID + 线程ID);}...
}

首先执行Redis的exists命令，判断key为锁名的Hash值是否不存在，也就是判断key为锁名myLock的Hash值是否存在。

一.如果key为锁名的Hash值不存在，那么就进行如下加锁处理

首先通过Redis的hset命令设置一个key为锁名的Hash值。该Hash值的key为锁名，value是一个映射。也就是在value值中会有一个field为UUID + 线程ID，value为1的映射。比如：hset myLock UUID:ThreadID 1，lua脚本中的ARGV[2]就是由UUID + 线程ID组成的唯一值。

然后通过Redis的pexpire命令设置key为锁名的Hash值的过期时间，也就是设置key为锁名的Hash值的过期时间为30秒。比如：pexpire myLock 30000。所以默认情况下，myLock这个锁在30秒后就会自动过期。

二.如果key为锁名的Hash值存在，那么就执行如下判断处理

首先通过Redis的hexists命令判断在key为锁名的Hash值里，field为UUID + 线程ID的映射是否已经存在。

如果在key为锁名的Hash值里，field为UUID + 线程ID的映射存在，那么就通过Redis的hincrby命令，对field为UUID + 线程ID的value值进行递增1。比如：hincrby myLock UUID:ThreadID 1。也就是在key为myLock的Hash值里，把field为UUID:ThreadID的value值从1累加到2，发生这种情况的时候往往就是当前线程对锁进行了重入。接着执行：pexpire myLock 30000，再次将myLock的有效期设置为30秒。

如果在key为锁名的Hash值里，field为UUID + 线程ID的映射不存在，发生这种情况的时候往往就是其他线程获取不到这把锁而产生互斥。那么就通过Redis的pttl命令，返回key为锁名的Hash值的剩余存活时间，因为不同线程的ARGV[2]是不一样的，ARGV[2] = UUID + 线程ID。

(4)执行加锁lua脚本的命令执行器逻辑

在RedissonLock的tryLockInnerAsync()方法中，会通过RedissonBaseLock的evalWriteAsync()方法执行lua脚本，即通过CommandAsyncService的evalWriteAsync()方法执行lua脚本。

在CommandAsyncService的evalWriteAsync()方法中，首先会执行CommandAsyncService的getNodeSource()方法获取对应的节点。然后执行CommandAsyncService的evalAsync()方法来执行lua脚本。

在CommandAsyncService的getNodeSource()方法中，会根据key进行CRC16运算，然后再对16384取模，计算出key的slot值。然后根据这个slot值创建一个NodeSource实例进行返回。

在CommandAsyncService的evalAsync()方法中，会将获得的NodeSource实例封装到Redis执行器RedisExecutor里。然后执行RedisExecutor，实现将脚本请求发送给对应的Redis节点处理。

public abstract class RedissonBaseLock extends RedissonExpirable implements RLock {//从外部传入的：在创建实现了RedissonClient的Redisson实例时，初始化的命令执行器CommandExecutorfinal CommandAsyncExecutor commandExecutor;public RedissonBaseLock(CommandAsyncExecutor commandExecutor, String name) {super(commandExecutor, name);this.commandExecutor = commandExecutor;this.id = commandExecutor.getConnectionManager().getId();this.internalLockLeaseTime = commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout();this.entryName = id + ":" + name;}...protected <T> RFuture<T> evalWriteAsync(String key, Codec codec, RedisCommand<T> evalCommandType, String script, List<Object> keys, Object... params) {//获取可用的节点，并继续封装一个命令执行器CommandBatchServiceMasterSlaveEntry entry = commandExecutor.getConnectionManager().getEntry(getRawName());int availableSlaves = entry.getAvailableSlaves();CommandBatchService executorService = createCommandBatchService(availableSlaves);//通过CommandAsyncService.evalWriteAsync方法执行lua脚本RFuture<T> result = executorService.evalWriteAsync(key, codec, evalCommandType, script, keys, params);if (commandExecutor instanceof CommandBatchService) {return result;}//异步执行然后获取结果RFuture<BatchResult<?>> future = executorService.executeAsync();CompletionStage<T> f = future.handle((res, ex) -> {if (ex == null && res.getSyncedSlaves() != availableSlaves) {throw new CompletionException(new IllegalStateException("Only " + res.getSyncedSlaves() + " of " + availableSlaves + " slaves were synced"));}return result.getNow();});return new CompletableFutureWrapper<>(f);}private CommandBatchService createCommandBatchService(int availableSlaves) {if (commandExecutor instanceof CommandBatchService) {return (CommandBatchService) commandExecutor;}BatchOptions options = BatchOptions.defaults().syncSlaves(availableSlaves, 1, TimeUnit.SECONDS);return new CommandBatchService(commandExecutor, options);}...
}public class CommandBatchService extends CommandAsyncService {...public CommandBatchService(CommandAsyncExecutor executor, BatchOptions options) {this(executor.getConnectionManager(), options, executor.getObjectBuilder(), RedissonObjectBuilder.ReferenceType.DEFAULT);}private CommandBatchService(ConnectionManager connectionManager, BatchOptions options, RedissonObjectBuilder objectBuilder, RedissonObjectBuilder.ReferenceType referenceType) {super(connectionManager, objectBuilder, referenceType);this.options = options;}...
}public class CommandAsyncService implements CommandAsyncExecutor {final ConnectionManager connectionManager;final RedissonObjectBuilder objectBuilder;final RedissonObjectBuilder.ReferenceType referenceType;public CommandAsyncService(ConnectionManager connectionManager, RedissonObjectBuilder objectBuilder, RedissonObjectBuilder.ReferenceType referenceType) {this.connectionManager = connectionManager;this.objectBuilder = objectBuilder;this.referenceType = referenceType;}...@Overridepublic <T, R> RFuture<R> evalWriteAsync(String key, Codec codec, RedisCommand<T> evalCommandType, String script, List<Object> keys, Object... params) {//获取key对应的节点NodeSource source = getNodeSource(key);//让对应的节点执行lua脚本请求return evalAsync(source, false, codec, evalCommandType, script, keys, false, params);}//获取key对应的Redis Cluster节点private NodeSource getNodeSource(String key) {//先计算key对应的slot值int slot = connectionManager.calcSlot(key);//返回节点实例return new NodeSource(slot);}//执行lua脚本private <T, R> RFuture<R> evalAsync(NodeSource nodeSource, boolean readOnlyMode, Codec codec, RedisCommand<T> evalCommandType, String script, List<Object> keys, boolean noRetry, Object... params) {if (isEvalCacheActive() && evalCommandType.getName().equals("EVAL")) {CompletableFuture<R> mainPromise = new CompletableFuture<>();Object[] pps = copy(params);CompletableFuture<R> promise = new CompletableFuture<>();String sha1 = calcSHA(script);RedisCommand cmd = new RedisCommand(evalCommandType, "EVALSHA");List<Object> args = new ArrayList<Object>(2 + keys.size() + params.length);args.add(sha1);args.add(keys.size());args.addAll(keys);args.addAll(Arrays.asList(params));//将根据key进行CRC16运算然后对16384取模获取到的NodeSource实例，封装到Redis执行器RedisExecutor中RedisExecutor<T, R> executor = new RedisExecutor<>(readOnlyMode, nodeSource, codec, cmd, args.toArray(), promise, false, connectionManager, objectBuilder, referenceType, noRetry);//通过执行Redis执行器RedisExecutor，来实现将lua脚本请求发送给对应的Redis节点进行处理executor.execute();...}...}...
}public class ClusterConnectionManager extends MasterSlaveConnectionManager {public static final int MAX_SLOT = 16384;//Redis Cluster默认有16384个slot...//对key进行CRC16运算，然后再对16384取模@Overridepublic int calcSlot(String key) {if (key == null) {return 0;}int start = key.indexOf('{');if (start != -1) {int end = key.indexOf('}');if (end != -1 && start + 1 < end) {key = key.substring(start + 1, end);}}int result = CRC16.crc16(key.getBytes()) % MAX_SLOT;return result;}...
}

(5)如何根据slot值获取对应的节点

因为最后会执行封装了NodeSource实例的RedisExecutor的excute()方法，而NodeSource实例中又会封装了锁名key对应的slot值，所以RedisExecutor的excute()方法可以通过getConnection()方法获取对应节点的连接。

其中RedisExecutor的getConnection()方法会调用到MasterSlaveConnectionManager的connectionWriteOp()方法，该方法又会通过调用ConnectionManager的getEntry()方法根据slot值获取节点，也就是由ClusterConnectionManager的getEntry()方法去获取Redis的主节点。

其实在初始化连接管理器ClusterConnectionManager时，就已经根据配置初始化好哪些slot映射到那个Redis主节点了。

public class RedisExecutor<V, R> {NodeSource source;...public void execute() {...//异步获取建立好的Redis连接CompletableFuture<RedisConnection> connectionFuture = getConnection().toCompletableFuture();...}protected CompletableFuture<RedisConnection> getConnection() {...connectionFuture = connectionManager.connectionWriteOp(source, command);return connectionFuture;}...
}public class MasterSlaveConnectionManager implements ConnectionManager {...@Overridepublic CompletableFuture<RedisConnection> connectionWriteOp(NodeSource source, RedisCommand<?> command) {MasterSlaveEntry entry = getEntry(source);...}private MasterSlaveEntry getEntry(NodeSource source) {if (source.getRedirect() != null) {return getEntry(source.getAddr());}MasterSlaveEntry entry = source.getEntry();if (source.getRedisClient() != null) {entry = getEntry(source.getRedisClient());}if (entry == null && source.getSlot() != null) {//根据slot获取Redis的主节点entry = getEntry(source.getSlot());}return entry;}...
}public class ClusterConnectionManager extends MasterSlaveConnectionManager {//slot和Redis主节点的原子映射数组private final AtomicReferenceArray<MasterSlaveEntry> slot2entry = new AtomicReferenceArray<>(MAX_SLOT);//Redis客户端连接和Redis主节点的映射关系private final Map<RedisClient, MasterSlaveEntry> client2entry = new ConcurrentHashMap<>();...@Overridepublic MasterSlaveEntry getEntry(int slot) {//根据slot获取Redis的主节点return slot2entry.get(slot);}...//初始化连接管理器ClusterConnectionManager时//就已经根据配置初始化好那些slot映射到那个Redis主节点了public ClusterConnectionManager(ClusterServersConfig cfg, Config config, UUID id) {...for (String address : cfg.getNodeAddresses()) {...CompletableFuture<Collection<ClusterPartition>> partitionsFuture = parsePartitions(nodes);Collection<ClusterPartition> partitions = partitionsFuture.join();List<CompletableFuture<Void>> masterFutures = new ArrayList<>();for (ClusterPartition partition : partitions) {...CompletableFuture<Void> masterFuture = addMasterEntry(partition, cfg);masterFutures.add(masterFuture);}...}...}private CompletableFuture<Void> addMasterEntry(ClusterPartition partition, ClusterServersConfig cfg) {...CompletionStage<RedisConnection> connectionFuture = connectToNode(cfg, partition.getMasterAddress(), configEndpointHostName);connectionFuture.whenComplete((connection, ex1) -> {//成功连接时的处理if (ex1 != null) {log.error("Can't connect to master: {} with slot ranges: {}", partition.getMasterAddress(), partition.getSlotRanges());result.completeExceptionally(ex1);return;}MasterSlaveServersConfig config = create(cfg);config.setMasterAddress(partition.getMasterAddress().toString());//创建Redis的主节点MasterSlaveEntry entry;if (config.checkSkipSlavesInit()) {entry = new SingleEntry(ClusterConnectionManager.this, config);} else {Set<String> slaveAddresses = partition.getSlaveAddresses().stream().map(r -> r.toString()).collect(Collectors.toSet());config.setSlaveAddresses(slaveAddresses);entry = new MasterSlaveEntry(ClusterConnectionManager.this, config);}CompletableFuture<RedisClient> f = entry.setupMasterEntry(new RedisURI(config.getMasterAddress()), configEndpointHostName);f.whenComplete((masterClient, ex3) -> {if (ex3 != null) {log.error("Can't add master: " + partition.getMasterAddress() + " for slot ranges: " + partition.getSlotRanges(), ex3);result.completeExceptionally(ex3);return;}//为创建的Redis的主节点添加slot值for (Integer slot : partition.getSlots()) {addEntry(slot, entry);lastPartitions.put(slot, partition);}...});});...}//添加slot到对应节点的映射关系private void addEntry(Integer slot, MasterSlaveEntry entry) {MasterSlaveEntry oldEntry = slot2entry.getAndSet(slot, entry);if (oldEntry != entry) {entry.incReference();shutdownEntry(oldEntry);}client2entry.put(entry.getClient(), entry);}...
}