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RedissonLock繼承結(jié)構(gòu)：

RLock接口中定義的方法：主要分析tryLock()實現(xiàn)。

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**(一) RedissonLock#tryLock:**加鎖邏輯

public boolean tryLock(long waitTime, long leaseTime, TimeUnit unit) throws InterruptedException {long time = unit.toMillis(waitTime);// 等待時間long current = System.currentTimeMillis();final long threadId = Thread.currentThread().getId();// 使用當(dāng)前線程ID，實現(xiàn)重入鎖Long ttl = tryAcquire(leaseTime, unit, threadId);// 嘗試獲取鎖// lock acquiredif (ttl == null) {// 沒有過期時間，未上鎖，直接返回獲取成功return true;}time -= (System.currentTimeMillis() - current);if (time <= 0) {// 等待時間已超時acquireFailed(threadId);return false;}current = System.currentTimeMillis();// 訂閱鎖的隊列，等待鎖被其余線程釋放后通知// 通過Redis的Channel訂閱監(jiān)聽隊列，subscribe內(nèi)部通過信號量semaphore，再通過await方法阻塞，內(nèi)部其實是用CountDownLatch來實現(xiàn)阻塞，獲取subscribe異步執(zhí)行的結(jié)果，來保證訂閱成功final RFuture<RedissonLockEntry> subscribeFuture = subscribe(threadId);if (!await(subscribeFuture, time, TimeUnit.MILLISECONDS)) {// 阻塞等待subscribe的future的結(jié)果對象(即分布式解鎖消息的結(jié)果)if (!subscribeFuture.cancel(false)) {subscribeFuture.addListener(new FutureListener<RedissonLockEntry>() {@Overridepublic void operationComplete(Future<RedissonLockEntry> future) throws Exception {if (subscribeFuture.isSuccess()) {unsubscribe(subscribeFuture, threadId);}}});}acquireFailed(threadId);return false;}try {time -= (System.currentTimeMillis() - current);if (time <= 0) {// subscribe方法調(diào)用超時，取消訂閱，不再繼續(xù)申請鎖acquireFailed(threadId);return false;}while (true) {long currentTime = System.currentTimeMillis();ttl = tryAcquire(leaseTime, unit, threadId);// 再次嘗試申請鎖if (ttl == null) {// 獲得鎖，返回return true;}time -= (System.currentTimeMillis() - currentTime);if (time <= 0) {// 超時acquireFailed(threadId);return false;}// waiting for message 等待訂閱的隊列消息currentTime = System.currentTimeMillis();// 通過信號量(共享鎖)阻塞,等待解鎖消息(這一點設(shè)計的非常精妙：減少了其他分布式節(jié)點的等待或者空轉(zhuǎn)等無效鎖申請的操作，整體提高了性能)if (ttl >= 0 && ttl < time) {// 在ttl內(nèi)，從Entry的信號量獲取一個許可(除非被中斷或者一直沒有可用的許可)getEntry(threadId).getLatch().tryAcquire(ttl, TimeUnit.MILLISECONDS);} else {// 在等待剩余時間內(nèi)...getEntry(threadId).getLatch().tryAcquire(time, TimeUnit.MILLISECONDS);}time -= (System.currentTimeMillis() - currentTime);if (time <= 0) {// 超時acquireFailed(threadId);return false;}}} finally {unsubscribe(subscribeFuture, threadId);// 無論是否獲得鎖,都要取消訂閱解鎖消息} // return get(tryLockAsync(waitTime, leaseTime, unit)); } ## RedissonLock#getEntry -> RedissonLock#getEntryName protected String getEntryName() {return id + ":" + getName();// 客戶端實例ID+鎖名稱來保證多個實例下的鎖可重入 }

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0x0001:**RedissonLock#tryAcquire:**嘗試獲取鎖

private Long tryAcquire(long leaseTime, TimeUnit unit, long threadId) {return get(tryAcquireAsync(leaseTime, unit, threadId)); } ## RedissonObject#get protected final CommandAsyncExecutor commandExecutor; protected final <V> V get(RFuture<V> future) {return commandExecutor.get(future); }

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0x0010:**RedissonLock#tryAcquireAsync:**異步嘗試獲取鎖，異步調(diào)用，get方法阻塞

## RedissonLock#tryAcquireAsync private <T> RFuture<Long> tryAcquireAsync(long leaseTime, TimeUnit unit, final long threadId) {if (leaseTime != -1) {// 起租時間不為空return tryLockInnerAsync(leaseTime, unit, threadId, RedisCommands.EVAL_LONG);}// lockWatchdogTimeout = 30 * 1000默認30秒RFuture<Long> ttlRemainingFuture = tryLockInnerAsync(commandExecutor.getConnectionManager().getCfg().getLockWatchdogTimeout(), TimeUnit.MILLISECONDS, threadId, RedisCommands.EVAL_LONG);ttlRemainingFuture.addListener(new FutureListener<Long>() {@Overridepublic void operationComplete(Future<Long> future) throws Exception {if (!future.isSuccess()) {return;}Long ttlRemaining = future.getNow();if (ttlRemaining == null) {// 拿到鎖scheduleExpirationRenewal(threadId);}}});return ttlRemainingFuture; } ## RedissonLock#scheduleExpirationRenewal Redisson避免死鎖方案，避免鎖未被釋放。 ## 若未設(shè)置過期時間的話，redission默認的過期時間是30s，同時未避免鎖在業(yè)務(wù)未處理完成之前被提前釋放，Redisson在獲取到鎖且默認過期時間的時候，會在當(dāng)前客戶端內(nèi)部啟動一個定時任務(wù)，每隔internalLockLeaseTime/3的時間去刷新key的過期時間，這樣既避免了鎖提前釋放，同時如果客戶端宕機的話，這個鎖最多存活30s的時間就會自動釋放 if (expirationRenewalMap.containsKey(getEntryName())) {return; } Timeout task = commandExecutor.getConnectionManager().newTimeout(new TimerTask() {@Overridepublic void run(Timeout timeout) throws Exception {RFuture<Boolean> future = commandExecutor.evalWriteAsync(getName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,"if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) then " +"redis.call('pexpire', KEYS[1], ARGV[1]); " +"return 1; " +"end; " +"return 0;",Collections.<Object>singletonList(getName()), internalLockLeaseTime, getLockName(threadId));future.addListener(new FutureListener<Boolean>() {@Overridepublic void operationComplete(Future<Boolean> future) throws Exception {expirationRenewalMap.remove(getEntryName());if (!future.isSuccess()) {log.error("Can't update lock " + getName() + " expiration", future.cause());return;}if (future.getNow()) {// reschedule itselfscheduleExpirationRenewal(threadId);}}});} }, internalLockLeaseTime / 3, TimeUnit.MILLISECONDS); if (expirationRenewalMap.putIfAbsent(getEntryName(), task) != null) {task.cancel(); }

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0x0011:**CommandAsyncService#get:**包裝了CountDownLatch是為了支持線程可中斷操作

public <V> V get(RFuture<V> future) {if (!future.isDone()) {// Task還沒執(zhí)行完成final CountDownLatch l = new CountDownLatch(1);// 設(shè)置一個單線程的同步控制器future.addListener(new FutureListener<V>() {@Overridepublic void operationComplete(Future<V> future) throws Exception {l.countDown();// 操作完成}});boolean interrupted = false;while (!future.isDone()) {try {l.await();} catch (InterruptedException e) {interrupted = true;break;}}if (interrupted) {Thread.currentThread().interrupt();}}// commented out due to blocking issues up to 200 ms per minute for each thread// future.awaitUninterruptibly();if (future.isSuccess()) {return future.getNow();}throw convertException(future); }

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0x0100:**RedissonLock#tryLockInnerAsync:**真正執(zhí)行的是一段具有原子性的Lua腳本，并且最終也是由CommandAsynExecutor去執(zhí)行。使用Lua的好處：Redis會將整個腳本作為一個整體執(zhí)行，中間不會被其他命令插入。因此在編寫腳本的過程中無需擔(dān)心會出現(xiàn)競態(tài)條件，無需使用事務(wù)。

<T> RFuture<T> tryLockInnerAsync(long leaseTime, TimeUnit unit, long threadId, RedisStrictCommand<T> command) {internalLockLeaseTime = unit.toMillis(leaseTime);// 鎖過期時間-毫秒// getName() - 邏輯鎖名稱：比如方法名+名稱return commandExecutor.evalWriteAsync(getName(), LongCodec.INSTANCE, command,"Lua腳本",Collections.<Object>singletonList(getName()), internalLockLeaseTime, getLockName(threadId)); } ## RedissonLock#getLockName 鎖對應(yīng)的線程級別的名稱，支持相同線程可重入，不同線程不可重入 protected String getLockName(long threadId) {return id + ":" + threadId; }

????鎖的實際存儲類型是hash。KEY[1]->邏輯鎖名稱 ARGV[2]->線程級別的鎖名稱

if (redis.call('exists', KEYS[1]) == 0) thenredis.call('hset', KEYS[1], ARGV[2], 1);redis.call('pexpire', KEYS[1], ARGV[1]);return nil; end; if (redis.call('hexists', KEYS[1], ARGV[2]) == 1) thenredis.call('hincrby', KEYS[1], ARGV[2], 1);redis.call('pexpire', KEYS[1], ARGV[1]);return nil; end; return redis.call('pttl', KEYS[1]);

????分析這段Lua腳本：

• 檢查鎖名稱是否存在，如果不存在，獲取成功，同時設(shè)置線程級別鎖名稱，設(shè)置過期時間為internalLockLeaseTime
• 如果檢查存在KEYS[1], ARGV[2]，獲取成功，自增1,記錄重入的次數(shù)，更新過期時間
• 如果key不存在，直接返回key的剩余過期時間

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0x0101:**RedissonLock#acquireFailed:**把該線程從獲取鎖操作的等待隊列中直接刪掉

private void acquireFailed(long threadId) {get(acquireFailedAsync(threadId)); } ## RedissonFairLock#acquireFailedAsync @Override protected RFuture<Void> acquireFailedAsync(long threadId) {return commandExecutor.evalWriteAsync(getName(), LongCodec.INSTANCE, RedisCommands.EVAL_VOID,"local firstThreadId = redis.call('lindex', KEYS[1], 0); " + "if firstThreadId == ARGV[1] then " + "local keys = redis.call('zrange', KEYS[2], 0, -1); " + "for i = 1, #keys, 1 do " + "redis.call('zincrby', KEYS[2], -tonumber(ARGV[2]), keys[i]);" + "end;" + "end;" +"redis.call('zrem', KEYS[2], ARGV[1]); " +"redis.call('lrem', KEYS[1], 0, ARGV[1]); ",Arrays.<Object>asList(threadsQueueName, timeoutSetName), getLockName(threadId), threadWaitTime); }

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0x0110:**PublishSubscribe#subscribe:**訂閱消息

final AtomicReference<Runnable> listenerHolder = new AtomicReference<Runnable>(); // 根據(jù)channelName拿到信號量,channelName=UUID+":"+name,對應(yīng)一個鎖 final AsyncSemaphore semaphore = subscribeService.getSemaphore(new ChannelName(channelName)); final RPromise<E> newPromise = new RedissonPromise<E>() {@Overridepublic boolean cancel(boolean mayInterruptIfRunning) {return semaphore.remove(listenerHolder.get());} }; Runnable listener = new Runnable() {@Overridepublic void run() {E entry = entries.get(entryName);if (entry != null) {entry.aquire();semaphore.release();entry.getPromise().addListener(new TransferListener<E>(newPromise));return;}E value = createEntry(newPromise);value.aquire();E oldValue = entries.putIfAbsent(entryName, value);if (oldValue != null) {oldValue.aquire();semaphore.release();oldValue.getPromise().addListener(new TransferListener<E>(newPromise));return;}RedisPubSubListener<Object> listener = createListener(channelName, value);subscribeService.subscribe(LongCodec.INSTANCE, channelName, semaphore, listener);} }; // 把生成的監(jiān)聽線程listenser加入到信號量的監(jiān)聽集合中去，后面發(fā)布解鎖消息的時候，會喚醒 semaphore.acquire(listener); listenerHolder.set(listener); return newPromise;

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**(二) RedissonLock#unlock:**解鎖邏輯

@Override public void unlock() {try {get(unlockAsync(Thread.currentThread().getId()));} catch (RedisException e) {...} }

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0x0001:**RedissonLock#unlockAsync:**異步解鎖

@Override public RFuture<Void> unlockAsync(final long threadId) {final RPromise<Void> result = new RedissonPromise<Void>();RFuture<Boolean> future = unlockInnerAsync(threadId);// 此處Redis實現(xiàn)future.addListener(new FutureListener<Boolean>() {@Overridepublic void operationComplete(Future<Boolean> future) throws Exception {if (!future.isSuccess()) {cancelExpirationRenewal(threadId);result.tryFailure(future.cause());return;}Boolean opStatus = future.getNow();if (opStatus == null) {IllegalMonitorStateException cause = new IllegalMonitorStateException("attempt to unlock lock, not locked by current thread by node id: "+ id + " thread-id: " + threadId);result.tryFailure(cause);return;}if (opStatus) {// 解鎖成功之后取消更新鎖expire的時間任務(wù),針對于沒有鎖過期時間的cancelExpirationRenewal(null);}result.trySuccess(null);}});return result; }

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0x0010:**RedissonLock#unlockInnerAsync:**當(dāng)其他線程釋放鎖的時候，會同時根據(jù)鎖的唯一通道publish一條分布式的解鎖信息，接收到分布式消息后， 等待獲取鎖的Semaphore中的監(jiān)聽隊列中的listenser線程可重新申請鎖。

protected RFuture<Boolean> unlockInnerAsync(long threadId) {return commandExecutor.evalWriteAsync(getName(), LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,"Lua腳本",Arrays.<Object>asList(getName(), getChannelName()), LockPubSub.unlockMessage, internalLockLeaseTime, getLockName(threadId)); }

????拿出來Lua看看如何實現(xiàn)的：KEY[1]->邏輯鎖名稱 KEY[2]->getChannelName() ARGV[1]->0L ARGV[2]->過期時間 ARGV[3]->線程級別的鎖名稱

if (redis.call('exists', KEYS[1]) == 0) thenredis.call('publish', KEYS[2], ARGV[1]);return 1; end; if (redis.call('hexists', KEYS[1], ARGV[3]) == 0) thenreturn nil; end; local counter = redis.call('hincrby', KEYS[1], ARGV[3], -1); if (counter > 0) thenredis.call('pexpire', KEYS[1], ARGV[2]);return 0; elseredis.call('del', KEYS[1]);redis.call('publish', KEYS[2], ARGV[1]);return 1; end; return nil;

????分析這段Lua腳本：

• 如果鍵不存在，說明鎖可以用了，發(fā)布鎖釋放消息后返回
• 如果鎖不是被當(dāng)前線程鎖定，則返回nil
• Redisson支持重入，在解鎖的時候，引用數(shù)減1
• 如果重入數(shù)>0，重新設(shè)置過期時間
• 如果重入數(shù)>=0，說明鎖可以使用了，發(fā)布鎖釋放消息后返回

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**(三) LockPubSub#unlockMessage:**處理解鎖消息

Redisson在LockPubSub中處理解鎖消息，首先看一下LockPubSub繼承結(jié)構(gòu)：

PublishSubscribe#createListener

// 模板方法，提供給子類實現(xiàn) protected abstract void onMessage(E value, Long message);private RedisPubSubListener<Object> createListener(final String channelName, final E value) {RedisPubSubListener<Object> listener = new BaseRedisPubSubListener() {@Overridepublic void onMessage(CharSequence channel, Object message) {if (!channelName.equals(channel.toString())) {return;}PublishSubscribe.this.onMessage(value, (Long)message);// 此處會調(diào)用到LockPubSub.onMessage}...};return listener; }

**LockPubSub：**解鎖消息

public class LockPubSub extends PublishSubscribe<RedissonLockEntry> {public static final Long unlockMessage = 0L;// 解鎖消息，redis執(zhí)行l(wèi)ua返回值public static final Long readUnlockMessage = 1L;@Overrideprotected RedissonLockEntry createEntry(RPromise<RedissonLockEntry> newPromise) {return new RedissonLockEntry(newPromise);}@Overrideprotected void onMessage(RedissonLockEntry value, Long message) {if (message.equals(unlockMessage)) {// 解鎖消息Runnable runnableToExecute = value.getListeners().poll();if (runnableToExecute != null) {runnableToExecute.run();}// 釋放一個，喚醒等待的entry.getLatch().tryAcquire去再次嘗試獲取鎖value.getLatch().release();} else if (message.equals(readUnlockMessage)) {while (true) {// 如果還有其他Listeners回調(diào)，也喚醒執(zhí)行Runnable runnableToExecute = value.getListeners().poll();if (runnableToExecute == null) {break;}runnableToExecute.run();}value.getLatch().release(value.getLatch().getQueueLength());}} }

轉(zhuǎn)載于:https://my.oschina.net/javamaster/blog/3006215

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