在使用redisson消息订阅时，我针对门店商品库存减扣进行订阅的操作(在这里一个商品一个监听队列)，当正式投入生产时，发现一直再报Subscribe timeout: (" + timeout + "ms). Increase 'subscriptionsPerConnection' and/or 'subscriptionConnectionPoolSize' parameters.的错误，索性根据提示翻了翻源码看看原因：

在redisson里先关注一个类：RedisPubSubConnection该类继承自RedisConnection，根据名字我们可知它是一个典型的发布与订阅的类。那么在redisson使用时，会使用PubSubConnectionEntry进行一次包装：

public class PubSubConnectionEntry {            private final AtomicInteger subscribedChannelsAmount;        private final RedisPubSubConnection conn;            private final ConcurrentMap
    
      subscribeChannelListeners = new ConcurrentHashMap
     
      ();        private final ConcurrentMap
      
       >> channelListeners = new ConcurrentHashMap
       
        >>();            public PubSubConnectionEntry(RedisPubSubConnection conn, int subscriptionsPerConnection) {            super();            this.conn = conn;            this.subscribedChannelsAmount = new AtomicInteger(subscriptionsPerConnection);        }           //.....省略其他代码     }
       
      
     
    

在这里我们可以看到其有一个比较重要的属性 subscribedChannelsAmount，而这个值就是通过PublishSubscribeService进行调用的：

private void connect(final Codec codec, final ChannelName channelName,                final RPromise
    
      promise, final PubSubType type, final AsyncSemaphore lock, final RedisPubSubListener
     ... listeners) {          //....                                 RedisPubSubConnection conn = future.getNow();                                        final PubSubConnectionEntry entry = new PubSubConnectionEntry(conn, config.getSubscriptionsPerConnection());                    entry.tryAcquire();          //....        }
    

那么此属性就是根据config的subscriptionsPerConnection里设置的，那么此值就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;                }            }        }

如果当此值为0时，那么会重新获取一个可用的连接，代码如下：

int remainFreeAmount = freeEntry.tryAcquire();                    if (remainFreeAmount == -1) {                        throw new IllegalStateException();                    }                                        final PubSubConnectionEntry oldEntry = name2PubSubConnection.putIfAbsent(channelName, freeEntry);                    if (oldEntry != null) {                        freeEntry.release();                        freePubSubLock.release();                        subscribe(channelName, promise, type, lock, oldEntry, listeners);                        return;                    }                                        if (remainFreeAmount == 0) {                        freePubSubConnections.poll();                    }                    freePubSubLock.release();

如果此时没有可用的连接的话，恐怕此次操作就会等待新的连接直至超时，超时了就报上述的错误了，不过根据提示。我们此时的解决办法是增大subscriptionsPerConnection或者subscriptionConnectionPoolSize的值。当我们使用springboot时可以通过设置spring.redis.redisson.config(具体设置请参考)来指定redisson的配置文件或者重新创建RedissonClient:

@Bean(destroyMethod = "shutdown")            public RedissonClient redisson(RedissonProperties redissonProperties, RedisProperties redisProperties) throws IOException {                    Config config = new Config();                String prefix = "redis://";                Method method = ReflectionUtils.findMethod(RedisProperties.class, "isSsl");                if (method != null && (Boolean) ReflectionUtils.invokeMethod(method, redisProperties)) {                    prefix = "rediss://";                }                    config.useSingleServer()                        .setAddress(prefix + redisProperties.getHost() + ":" + redisProperties.getPort())                        .setConnectTimeout(30000).setSubscriptionsPerConnection(5000) //在这里指定数目                        .setDatabase(redisProperties.getDatabase())                        .setPassword(redisProperties.getPassword());                    return Redisson.create(config);            }