谢评论区 kangsong 指正，文章已更新

先贴一下异常信息

02-28 15:07:21.156 1975-2791/com.tencent.mm E/Xposed: [15:07:21]: publish failed, message: aaaa
                                                      正在进行过多的发布 (32202)
                                                          at org.eclipse.paho.client.mqttv3.internal.ClientState.send(ClientState.java:496)
                                                          at org.eclipse.paho.client.mqttv3.internal.ClientComms.internalSend(ClientComms.java:132)
                                                          at org.eclipse.paho.client.mqttv3.internal.ClientComms.sendNoWait(ClientComms.java:156)
                                                          at org.eclipse.paho.client.mqttv3.MqttAsyncClient.publish(MqttAsyncClient.java:1027)
                                                          at org.eclipse.paho.client.mqttv3.MqttClient.publish(MqttClient.java:399)
                                                          at io.communet.ichater.emq.util.MqttUtil.publishMsg(MqttUtil.java:171)
                                                          at io.communet.ichater.emq.util.MqttUtil.publishMsg(MqttUtil.java:161)
                                                          at io.communet.ichater.emq.sub.MqttSendMsgEventSubscribe.onEvent(MqttSendMsgEventSubscribe.java:28)
                                                          at java.lang.reflect.Method.invoke(Native Method)
                                                          at java.lang.reflect.Method.invoke(Method.java:372)
                                                          at org.greenrobot.eventbus.EventBus.invokeSubscriber(EventBus.java:507)
                                                          at org.greenrobot.eventbus.EventBus.invokeSubscriber(EventBus.java:501)
                                                          at org.greenrobot.eventbus.AsyncPoster.run(AsyncPoster.java:46)
                                                          at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
                                                          at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
                                                          at java.lang.Thread.run(Thread.java:818)

原因

根据堆栈信息找到报错地方

if (actualInFlight >= this.maxInflight) {
    //@TRACE 613= sending {0} msgs at max inflight window
    log.fine(CLASS_NAME, methodName, "613", new Object[]{new Integer(actualInFlight)});

    throw new MqttException(MqttException.REASON_CODE_MAX_INFLIGHT);
}

其中 actualInFlight 如下

// processed until the inflight window has space. 
if (actualInFlight < this.maxInflight) {
    // The in flight window is not full so process the 
    // first message in the queue
    result = (MqttWireMessage)pendingMessages.elementAt(0);
    pendingMessages.removeElementAt(0);
    actualInFlight++;
    
    //@TRACE 623=+1 actualInFlight={0}
    log.fine(CLASS_NAME,methodName,"623",new Object[]{new Integer(actualInFlight)});
}

从 pendingMessages 中取出消息时, actualInFlight 加 1, maxInflight 可以自己设定, 默认值为 10.

public class ClientState {
  ...
  volatile private Vector pendingMessages;
  ...
}

在 ClientState 中：

public void send(MqttWireMessage message, MqttToken token) throws MqttException {
        ... 
        if (message instanceof MqttPublish) {
            synchronized (queueLock) {
                if (actualInFlight >= this.maxInflight) {
                    //@TRACE 613= sending {0} msgs at max inflight window
                    log.fine(CLASS_NAME, methodName, "613", new Object[]{new Integer(actualInFlight)});

                    throw new MqttException(MqttException.REASON_CODE_MAX_INFLIGHT);
                }
                
                MqttMessage innerMessage = ((MqttPublish) message).getMessage();
                //@TRACE 628=pending publish key={0} qos={1} message={2}
                log.fine(CLASS_NAME,methodName,"628", new Object[]{new Integer(message.getMessageId()), new Integer(innerMessage.getQos()), message});

                switch(innerMessage.getQos()) {
                    case 2:
                        outboundQoS2.put(new Integer(message.getMessageId()), message);
                        persistence.put(getSendPersistenceKey(message), (MqttPublish) message);
                        break;
                    case 1:
                        outboundQoS1.put(new Integer(message.getMessageId()), message);
                        persistence.put(getSendPersistenceKey(message), (MqttPublish) message);
                        break;
                }
                tokenStore.saveToken(token, message);
                pendingMessages.addElement(message);
                queueLock.notifyAll();
            }
        } else {
        ...
        }
    }

可以看到 pendingMessages 中添加元素的时候并没有做 qos 类型的判断

private void decrementInFlight() {
    final String methodName = "decrementInFlight";
    synchronized (queueLock) {
        actualInFlight--;
        //@TRACE 646=-1 actualInFlight={0}
        log.fine(CLASS_NAME,methodName,"646",new Object[]{new Integer(actualInFlight)});
            
        if (!checkQuiesceLock()) {
            queueLock.notifyAll();
        }
    }
}

当收到消息反馈时 actualInFlight 减 1.

解决办法

1. 消息发送发送限流
2. 用单独的一个线程来完成 MQ 消息的推送

题外话

笔者出现这个错误是因为使用 EventBus, 之前使用单独线程的 Handler 是没有问题的, 调查发现, 使用 EventBus 是新建线程运行的, 而 Handler 是单独一个线程.

所以当发送大量消息的时候, EventBus 几乎是同一个点发出去, 就会造成这个错误