關於使用Redisson訂閱數問題
一、前提
最近在使用分佈式鎖redisson時遇到一個線上問題:發現是subscriptionsPerConnection or subscriptionConnectionPoolSize
的大小不夠,需要提高配置才能解決。
二、源碼分析
下面對其源碼進行分析,才能找到到底是什麼邏輯導致問題所在:
1、RedissonLock#lock() 方法
private void lock(long leaseTime, TimeUnit unit, boolean interruptibly) throws InterruptedException { long threadId = Thread.currentThread().getId(); // 嘗試獲取,如果ttl == null,則表示獲取鎖成功 Long ttl = tryAcquire(leaseTime, unit, threadId); // lock acquired if (ttl == null) { return; } // 訂閱鎖釋放事件,並通過await方法阻塞等待鎖釋放,有效的解決瞭無效的鎖申請浪費資源的問題 RFuture<RedissonLockEntry> future = subscribe(threadId); if (interruptibly) { commandExecutor.syncSubscriptionInterrupted(future); } else { commandExecutor.syncSubscription(future); } // 後面代碼忽略 try { // 無限循環獲取鎖,直到獲取鎖成功 // ... } finally { // 取消訂閱鎖釋放事件 unsubscribe(future, threadId); } }
總結下主要邏輯:
- 獲取當前線程的線程id;
- tryAquire嘗試獲取鎖,並返回ttl
- 如果ttl為空,則結束流程;否則進入後續邏輯;
- this.subscribe(threadId)訂閱當前線程,返回一個RFuture;
- 如果在指定時間沒有監聽到,則會產生如上異常。
- 訂閱成功後, 通過while(true)循環,一直嘗試獲取鎖
- fially代碼塊,會解除訂閱
所以上述這情況問題應該出現在subscribe()方法中
2、詳細看下subscribe()方法
protected RFuture<RedissonLockEntry> subscribe(long threadId) { // entryName 格式:“id:name”; // channelName 格式:“redisson_lock__channel:name”; return pubSub.subscribe(getEntryName(), getChannelName()); }
RedissonLock#pubSub 是在RedissonLock構造函數中初始化的:
public RedissonLock(CommandAsyncExecutor commandExecutor, String name) { // .... this.pubSub = commandExecutor.getConnectionManager().getSubscribeService().getLockPubSub(); }
而subscribeService在MasterSlaveConnectionManager的實現中又是通過如下方式構造的
public MasterSlaveConnectionManager(MasterSlaveServersConfig cfg, Config config, UUID id) { this(config, id); this.config = cfg; // 初始化 initTimer(cfg); initSingleEntry(); } protected void initTimer(MasterSlaveServersConfig config) { int[] timeouts = new int[]{config.getRetryInterval(), config.getTimeout()}; Arrays.sort(timeouts); int minTimeout = timeouts[0]; if (minTimeout % 100 != 0) { minTimeout = (minTimeout % 100) / 2; } else if (minTimeout == 100) { minTimeout = 50; } else { minTimeout = 100; } timer = new HashedWheelTimer(new DefaultThreadFactory("redisson-timer"), minTimeout, TimeUnit.MILLISECONDS, 1024, false); connectionWatcher = new IdleConnectionWatcher(this, config); // 初始化:其中this就是MasterSlaveConnectionManager實例,config則為MasterSlaveServersConfig實例: subscribeService = new PublishSubscribeService(this, config); }
PublishSubscribeService構造函數
private final SemaphorePubSub semaphorePubSub = new SemaphorePubSub(this); public PublishSubscribeService(ConnectionManager connectionManager, MasterSlaveServersConfig config) { super(); this.connectionManager = connectionManager; this.config = config; for (int i = 0; i < locks.length; i++) { // 這裡初始化瞭一組信號量,每個信號量的初始值為1 locks[i] = new AsyncSemaphore(1); } }
3、回到subscribe()方法主要邏輯還是交給瞭 LockPubSub#subscribe()裡面
private final ConcurrentMap<String, E> entries = new ConcurrentHashMap<>(); public RFuture<E> subscribe(String entryName, String channelName) { // 從PublishSubscribeService獲取對應的信號量。 相同的channelName獲取的是同一個信號量 // public AsyncSemaphore getSemaphore(ChannelName channelName) { // return locks[Math.abs(channelName.hashCode() % locks.length)]; // } AsyncSemaphore semaphore = service.getSemaphore(new ChannelName(channelName)); AtomicReference<Runnable> listenerHolder = new AtomicReference<Runnable>(); RPromise<E> newPromise = new RedissonPromise<E>() { @Override public boolean cancel(boolean mayInterruptIfRunning) { return semaphore.remove(listenerHolder.get()); } }; Runnable listener = new Runnable() { @Override public void run() { // 如果存在RedissonLockEntry, 則直接利用已有的監聽 E entry = entries.get(entryName); if (entry != null) { entry.acquire(); semaphore.release(); entry.getPromise().onComplete(new TransferListener<E>(newPromise)); return; } E value = createEntry(newPromise); value.acquire(); E oldValue = entries.putIfAbsent(entryName, value); if (oldValue != null) { oldValue.acquire(); semaphore.release(); oldValue.getPromise().onComplete(new TransferListener<E>(newPromise)); return; } // 創建監聽, RedisPubSubListener<Object> listener = createListener(channelName, value); // 訂閱監聽 service.subscribe(LongCodec.INSTANCE, channelName, semaphore, listener); } }; // 最終會執行listener.run方法 semaphore.acquire(listener); listenerHolder.set(listener); return newPromise; }
AsyncSemaphore#acquire()方法
public void acquire(Runnable listener) { acquire(listener, 1); } public void acquire(Runnable listener, int permits) { boolean run = false; synchronized (this) { // counter初始化值為1 if (counter < permits) { // 如果不是第一次執行,則將listener加入到listeners集合中 listeners.add(new Entry(listener, permits)); return; } else { counter -= permits; run = true; } } // 第一次執行acquire, 才會執行listener.run()方法 if (run) { listener.run(); } }
梳理上述邏輯:
1、從PublishSubscribeService獲取對應的信號量, 相同的channelName獲取的是同一個信號量
2、如果是第一次請求,則會立馬執行listener.run()方法, 否則需要等上個線程獲取到該信號量執行完方能執行;
3、如果已經存在RedissonLockEntry, 則利用已經訂閱就行
4、如果不存在RedissonLockEntry, 則會創建新的RedissonLockEntry,然後進行。
從上面代碼看,主要邏輯是交給瞭PublishSubscribeService#subscribe方法
4、PublishSubscribeService#subscribe邏輯如下:
private final ConcurrentMap<ChannelName, PubSubConnectionEntry> name2PubSubConnection = new ConcurrentHashMap<>(); private final Queue<PubSubConnectionEntry> freePubSubConnections = new ConcurrentLinkedQueue<>(); public RFuture<PubSubConnectionEntry> subscribe(Codec codec, String channelName, AsyncSemaphore semaphore, RedisPubSubListener<?>... listeners) { RPromise<PubSubConnectionEntry> promise = new RedissonPromise<PubSubConnectionEntry>(); // 主要邏輯入口, 這裡要主要channelName每次都是新對象, 但內部覆寫hashCode+equals。 subscribe(codec, new ChannelName(channelName), promise, PubSubType.SUBSCRIBE, semaphore, listeners); return promise; } private void subscribe(Codec codec, ChannelName channelName, RPromise<PubSubConnectionEntry> promise, PubSubType type, AsyncSemaphore lock, RedisPubSubListener<?>... listeners) { PubSubConnectionEntry connEntry = name2PubSubConnection.get(channelName); if (connEntry != null) { // 從已有Connection中取,如果存在直接把listeners加入到PubSubConnectionEntry中 addListeners(channelName, promise, type, lock, connEntry, listeners); return; } // 沒有時,才是最重要的邏輯 freePubSubLock.acquire(new Runnable() { @Override public void run() { if (promise.isDone()) { lock.release(); freePubSubLock.release(); return; } // 從隊列中取頭部元素 PubSubConnectionEntry freeEntry = freePubSubConnections.peek(); if (freeEntry == null) { // 第一次肯定是沒有的需要建立 connect(codec, channelName, promise, type, lock, listeners); return; } // 如果存在則嘗試獲取,如果remainFreeAmount小於0則拋出異常終止瞭。 int remainFreeAmount = freeEntry.tryAcquire(); if (remainFreeAmount == -1) { throw new IllegalStateException(); } PubSubConnectionEntry oldEntry = name2PubSubConnection.putIfAbsent(channelName, freeEntry); if (oldEntry != null) { freeEntry.release(); freePubSubLock.release(); addListeners(channelName, promise, type, lock, oldEntry, listeners); return; } // 如果remainFreeAmount=0, 則從隊列中移除 if (remainFreeAmount == 0) { freePubSubConnections.poll(); } freePubSubLock.release(); // 增加監聽 RFuture<Void> subscribeFuture = addListeners(channelName, promise, type, lock, freeEntry, listeners); ChannelFuture future; if (PubSubType.PSUBSCRIBE == type) { future = freeEntry.psubscribe(codec, channelName); } else { future = freeEntry.subscribe(codec, channelName); } future.addListener(new ChannelFutureListener() { @Override public void operationComplete(ChannelFuture future) throws Exception { if (!future.isSuccess()) { if (!promise.isDone()) { subscribeFuture.cancel(false); } return; } connectionManager.newTimeout(new TimerTask() { @Override public void run(Timeout timeout) throws Exception { subscribeFuture.cancel(false); } }, config.getTimeout(), TimeUnit.MILLISECONDS); } }); } }); } private void connect(Codec codec, ChannelName channelName, RPromise<PubSubConnectionEntry> promise, PubSubType type, AsyncSemaphore lock, RedisPubSubListener<?>... listeners) { // 根據channelName計算出slot獲取PubSubConnection int slot = connectionManager.calcSlot(channelName.getName()); RFuture<RedisPubSubConnection> connFuture = nextPubSubConnection(slot); promise.onComplete((res, e) -> { if (e != null) { ((RPromise<RedisPubSubConnection>) connFuture).tryFailure(e); } }); connFuture.onComplete((conn, e) -> { if (e != null) { freePubSubLock.release(); lock.release(); promise.tryFailure(e); return; } // 這裡會從配置中讀取subscriptionsPerConnection PubSubConnectionEntry entry = new PubSubConnectionEntry(conn, config.getSubscriptionsPerConnection()); // 每獲取一次,subscriptionsPerConnection就會減直到為0 int remainFreeAmount = entry.tryAcquire(); // 如果舊的存在,則將現有的entry釋放,然後將listeners加入到oldEntry中 PubSubConnectionEntry oldEntry = name2PubSubConnection.putIfAbsent(channelName, entry); if (oldEntry != null) { releaseSubscribeConnection(slot, entry); freePubSubLock.release(); addListeners(channelName, promise, type, lock, oldEntry, listeners); return; } if (remainFreeAmount > 0) { // 加入到隊列中 freePubSubConnections.add(entry); } freePubSubLock.release(); RFuture<Void> subscribeFuture = addListeners(channelName, promise, type, lock, entry, listeners); // 這裡真正的進行訂閱(底層與redis交互) ChannelFuture future; if (PubSubType.PSUBSCRIBE == type) { future = entry.psubscribe(codec, channelName); } else { future = entry.subscribe(codec, channelName); } future.addListener(new ChannelFutureListener() { @Override public void operationComplete(ChannelFuture future) throws Exception { if (!future.isSuccess()) { if (!promise.isDone()) { subscribeFuture.cancel(false); } return; } connectionManager.newTimeout(new TimerTask() { @Override public void run(Timeout timeout) throws Exception { subscribeFuture.cancel(false); } }, config.getTimeout(), TimeUnit.MILLISECONDS); } }); }); }
PubSubConnectionEntry#tryAcquire方法, subscriptionsPerConnection代表瞭每個連接的最大訂閱數。當tryAcqcurie的時候會減少這個數量:
public int tryAcquire() { while (true) { int value = subscribedChannelsAmount.get(); if (value == 0) { return -1; } if (subscribedChannelsAmount.compareAndSet(value, value - 1)) { return value - 1; } } }
梳理上述邏輯:
1、還是進行重復判斷, 根據channelName從name2PubSubConnection中獲取,看是否存在已經訂閱:PubSubConnectionEntry; 如果存在直接把新的listener加入到PubSubConnectionEntry。
2、從隊列freePubSubConnections中取公用的PubSubConnectionEntry, 如果沒有就進入connect()方法
2.1 會根據subscriptionsPerConnection創建PubSubConnectionEntry, 然後調用其tryAcquire()方法 – 每調用一次就會減1
2.2 將新的PubSubConnectionEntry放入全局的name2PubSubConnection, 方便後續重復使用;
2.3 同時也將PubSubConnectionEntry放入隊列freePubSubConnections中。- remainFreeAmount > 0
2.4 後面就是進行底層的subscribe和addListener
3、如果已經存在PubSubConnectionEntry,則利用已有的PubSubConnectionEntry進行tryAcquire;
4、如果remainFreeAmount < 0 會拋出IllegalStateException異常;如果remainFreeAmount=0,則會將其從隊列中移除, 那麼後續請求會重新獲取一個可用的連接
5、最後也是進行底層的subscribe和addListener;
三 總結
根因: 從上面代碼分析, 導致問題的根因是因為PublishSubscribeService 會使用公共隊列中的freePubSubConnections, 如果同一個key一次性請求超過subscriptionsPerConnection它的默認值5時,remainFreeAmount就可能出現-1的情況, 那麼就會導致commandExecutor.syncSubscription(future)中等待超時,也就拋出如上異常Subscribe timeout: (7500ms). Increase 'subscriptionsPerConnection' and/or 'subscriptionConnectionPoolSize' parameters.
解決方法: 在初始化Redisson可以可指定這個配置項的值。
相關參數的解釋以及默認值請參考官網:https://github.com/redisson/redisson/wiki/2.-Configuration#23-common-settings
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