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使用Redisson订阅数问题怎么解决

发表于:2025-01-19 作者:千家信息网编辑
千家信息网最后更新 2025年01月19日,本文小编为大家详细介绍"使用Redisson订阅数问题怎么解决",内容详细,步骤清晰,细节处理妥当,希望这篇"使用Redisson订阅数问题怎么解决"文章能帮助大家解决疑惑,下面跟着小编的思路慢慢深入
千家信息网最后更新 2025年01月19日使用Redisson订阅数问题怎么解决

本文小编为大家详细介绍"使用Redisson订阅数问题怎么解决",内容详细,步骤清晰,细节处理妥当,希望这篇"使用Redisson订阅数问题怎么解决"文章能帮助大家解决疑惑,下面跟着小编的思路慢慢深入,一起来学习新知识吧。

    一、前提

    最近在使用分布式锁redisson时遇到一个线上问题:发现是subscriptionsPerConnection or subscriptionConnectionPoolSize 的大小不够,需要提高配置才能解决。

    二、源码分析

    下面对其源码进行分析,才能找到到底是什么逻辑导致问题所在:

    1、RedissonLock#lock() 方法

    private void lock(long leaseTime, TimeUnit unit, boolean interruptibly) throws InterruptedException {        long threadId = Thread.currentThread().getId();        // 尝试获取,如果ttl == null,则表示获取锁成功        Long ttl = tryAcquire(leaseTime, unit, threadId);        // lock acquired        if (ttl == null) {            return;        }        // 订阅锁释放事件,并通过await方法阻塞等待锁释放,有效的解决了无效的锁申请浪费资源的问题        RFuture future = subscribe(threadId);        if (interruptibly) {            commandExecutor.syncSubscriptionInterrupted(future);        } else {            commandExecutor.syncSubscription(future);        }        // 后面代码忽略        try {            // 无限循环获取锁,直到获取锁成功            // ...        } finally {            // 取消订阅锁释放事件            unsubscribe(future, threadId);        }}

    总结下主要逻辑:

    • 获取当前线程的线程id;

    • tryAquire尝试获取锁,并返回ttl

    • 如果ttl为空,则结束流程;否则进入后续逻辑;

    • this.subscribe(threadId)订阅当前线程,返回一个RFuture;

    • 如果在指定时间没有监听到,则会产生如上异常。

    • 订阅成功后, 通过while(true)循环,一直尝试获取锁

    • fially代码块,会解除订阅

    所以上述这情况问题应该出现在subscribe()方法中

    2、详细看下subscribe()方法

    protected RFuture 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构造函数中初始化的:

    public RedissonLock(CommandAsyncExecutor commandExecutor, String name) {    // ....    this.pubSub = commandExecutor.getConnectionManager().getSubscribeService().getLockPubSub();}

    而subscribeService在MasterSlaveConnectionManager的实现中又是通过如下方式构造的

    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实例,config则为MasterSlaveServersConfig实例:    subscribeService = new PublishSubscribeService(this, config);}

    PublishSubscribeService构造函数

    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++) {        // 这里初始化了一组信号量,每个信号量的初始值为1        locks[i] = new AsyncSemaphore(1);    }}

    3、回到subscribe()方法主要逻辑还是交给了 LockPubSub#subscribe()里面

    private final ConcurrentMap entries = new ConcurrentHashMap<>();public RFuture subscribe(String entryName, String channelName) {      // 从PublishSubscribeService获取对应的信号量。 相同的channelName获取的是同一个信号量     // public AsyncSemaphore getSemaphore(ChannelName channelName) {    //    return locks[Math.abs(channelName.hashCode() % locks.length)];    // }    AsyncSemaphore semaphore = service.getSemaphore(new ChannelName(channelName));    AtomicReference listenerHolder = new AtomicReference();        RPromise newPromise = new RedissonPromise() {        @Override        public boolean cancel(boolean mayInterruptIfRunning) {            return semaphore.remove(listenerHolder.get());        }    };    Runnable listener = new Runnable() {        @Override        public void run() {            //  如果存在RedissonLockEntry, 则直接利用已有的监听            E entry = entries.get(entryName);            if (entry != null) {                entry.acquire();                semaphore.release();                entry.getPromise().onComplete(new TransferListener(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(newPromise));                return;            }            // 创建监听,            RedisPubSubListener listener = createListener(channelName, value);            // 订阅监听            service.subscribe(LongCodec.INSTANCE, channelName, semaphore, listener);        }    };    // 最终会执行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初始化值为1        if (counter < permits) {            // 如果不是第一次执行,则将listener加入到listeners集合中            listeners.add(new Entry(listener, permits));            return;        } else {            counter -= permits;            run = true;        }    }    // 第一次执行acquire, 才会执行listener.run()方法    if (run) {        listener.run();    }}

    梳理上述逻辑:

    1、从PublishSubscribeService获取对应的信号量, 相同的channelName获取的是同一个信号量
    2、如果是第一次请求,则会立马执行listener.run()方法, 否则需要等上个线程获取到该信号量执行完方能执行;
    3、如果已经存在RedissonLockEntry, 则利用已经订阅就行
    4、如果不存在RedissonLockEntry, 则会创建新的RedissonLockEntry,然后进行。

    从上面代码看,主要逻辑是交给了PublishSubscribeService#subscribe方法

    4、PublishSubscribeService#subscribe逻辑如下:

    private final ConcurrentMap name2PubSubConnection = new ConcurrentHashMap<>();private final Queue freePubSubConnections = new ConcurrentLinkedQueue<>();public RFuture subscribe(Codec codec, String channelName, AsyncSemaphore semaphore, RedisPubSubListener... listeners) {    RPromise promise = new RedissonPromise();    // 主要逻辑入口, 这里要主要channelName每次都是新对象, 但内部覆写hashCode+equals。    subscribe(codec, new ChannelName(channelName), promise, PubSubType.SUBSCRIBE, semaphore, listeners);    return promise;}private void subscribe(Codec codec, ChannelName channelName,  RPromise promise, PubSubType type, AsyncSemaphore lock, RedisPubSubListener... listeners) {    PubSubConnectionEntry connEntry = name2PubSubConnection.get(channelName);    if (connEntry != null) {        // 从已有Connection中取,如果存在直接把listeners加入到PubSubConnectionEntry中        addListeners(channelName, promise, type, lock, connEntry, listeners);        return;    }    // 没有时,才是最重要的逻辑    freePubSubLock.acquire(new Runnable() {        @Override        public void run() {            if (promise.isDone()) {                lock.release();                freePubSubLock.release();                return;            }            // 从队列中取头部元素            PubSubConnectionEntry freeEntry = freePubSubConnections.peek();            if (freeEntry == null) {                // 第一次肯定是没有的需要建立                connect(codec, channelName, promise, type, lock, listeners);                return;            }            // 如果存在则尝试获取,如果remainFreeAmount小于0则抛出异常终止了。            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, 则从队列中移除            if (remainFreeAmount == 0) {                freePubSubConnections.poll();            }            freePubSubLock.release();            // 增加监听            RFuture 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 promise, PubSubType type, AsyncSemaphore lock, RedisPubSubListener... listeners) {    // 根据channelName计算出slot获取PubSubConnection    int slot = connectionManager.calcSlot(channelName.getName());    RFuture connFuture = nextPubSubConnection(slot);    promise.onComplete((res, e) -> {        if (e != null) {            ((RPromise) connFuture).tryFailure(e);        }    });    connFuture.onComplete((conn, e) -> {        if (e != null) {            freePubSubLock.release();            lock.release();            promise.tryFailure(e);            return;        }        // 这里会从配置中读取subscriptionsPerConnection        PubSubConnectionEntry entry = new PubSubConnectionEntry(conn, config.getSubscriptionsPerConnection());        // 每获取一次,subscriptionsPerConnection就会减直到为0        int remainFreeAmount = entry.tryAcquire();        // 如果旧的存在,则将现有的entry释放,然后将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) {            // 加入到队列中            freePubSubConnections.add(entry);        }        freePubSubLock.release();        RFuture subscribeFuture = addListeners(channelName, promise, type, lock, entry, listeners);        // 这里真正的进行订阅(底层与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代表了每个连接的最大订阅数。当tryAcqcurie的时候会减少这个数量:

     public int tryAcquire() {    while (true) {        int value = subscribedChannelsAmount.get();        if (value == 0) {            return -1;        }        if (subscribedChannelsAmount.compareAndSet(value, value - 1)) {            return value - 1;        }    }}

    梳理上述逻辑:

    1、还是进行重复判断, 根据channelName从name2PubSubConnection中获取,看是否存在已经订阅:PubSubConnectionEntry; 如果存在直接把新的listener加入到PubSubConnectionEntry。
    2、从队列freePubSubConnections中取公用的PubSubConnectionEntry, 如果没有就进入connect()方法

    2.1 会根据subscriptionsPerConnection创建PubSubConnectionEntry, 然后调用其tryAcquire()方法 - 每调用一次就会减1
    2.2 将新的PubSubConnectionEntry放入全局的name2PubSubConnection, 方便后续重复使用;
    2.3 同时也将PubSubConnectionEntry放入队列freePubSubConnections中。- remainFreeAmount > 0
    2.4 后面就是进行底层的subscribe和addListener

    3、如果已经存在PubSubConnectionEntry,则利用已有的PubSubConnectionEntry进行tryAcquire;
    4、如果remainFreeAmount < 0 会抛出IllegalStateException异常;如果remainFreeAmount=0,则会将其从队列中移除, 那么后续请求会重新获取一个可用的连接
    5、最后也是进行底层的subscribe和addListener;

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