发现问题

下面部分是io.moquette.spi.impl.BrokerInterceptor.java部分源码

@Override
    public void notifyClientConnected(final MqttConnectMessage msg) {
        for (final InterceptHandler handler : this.handlers.get(InterceptConnectMessage.class)) {
            LOG.debug("Sending MQTT CONNECT message to interceptor. CId={}, interceptorId={}",
                    msg.payload().clientIdentifier(), handler.getID());
            executor.execute(() -> handler.onConnect(new InterceptConnectMessage(msg)));
        }
    }

    @Override
    public void notifyClientDisconnected(final String clientID, final String username) {
        for (final InterceptHandler handler : this.handlers.get(InterceptDisconnectMessage.class)) {
            LOG.debug("Notifying MQTT client disconnection to interceptor. CId={}, username={}, interceptorId={}",
                clientID, username, handler.getID());
            executor.execute(() -> handler.onDisconnect(new InterceptDisconnectMessage(clientID, username)));
        }
    }

    @Override
    public void notifyClientConnectionLost(final String clientID, final String username) {
        for (final InterceptHandler handler : this.handlers.get(InterceptConnectionLostMessage.class)) {
            LOG.debug("Notifying unexpected MQTT client disconnection to interceptor CId={}, username={}, " +
                "interceptorId={}", clientID, username, handler.getID());
            executor.execute(() -> handler.onConnectionLost(new InterceptConnectionLostMessage(clientID, username)));
        }
    }

    @Override
    public void notifyTopicPublished(final MqttPublishMessage msg, final String clientID, final String username) {
        msg.retain();

        executor.execute(() -> {
                try {
                    int messageId = msg.variableHeader().messageId();
                    String topic = msg.variableHeader().topicName();
                    for (InterceptHandler handler : handlers.get(InterceptPublishMessage.class)) {
                        LOG.debug("Notifying MQTT PUBLISH message to interceptor. CId={}, messageId={}, topic={}, "
                                + "interceptorId={}", clientID, messageId, topic, handler.getID());
                        handler.onPublish(new InterceptPublishMessage(msg, clientID, username));
                    }
                } finally {
                    ReferenceCountUtil.release(msg);
                }
        });
    }

    @Override
    public void notifyTopicSubscribed(final Subscription sub, final String username) {
        for (final InterceptHandler handler : this.handlers.get(InterceptSubscribeMessage.class)) {
            LOG.debug("Notifying MQTT SUBSCRIBE message to interceptor. CId={}, topicFilter={}, interceptorId={}",
                sub.getClientId(), sub.getTopicFilter(), handler.getID());
            executor.execute(() -> handler.onSubscribe(new InterceptSubscribeMessage(sub, username)));
        }
    }

可以发现在除了notifyTopicPublished()，其它方法中，在for循环中每次for循环，对于InterceptHandler的调用都是在线程池中每次都是新执行一个任务，但是在notifyTopicPublished()方法中是在一个线程中for循环依次调用，这样处理首先没有用到线程池的多线程，其次是一旦某个InterceptHandler的notifyTopicPublished方法是阻塞的，那么后面的InterceptHandler的notifyTopicPublished()都会被阻塞。

优化逻辑

优化方向：向启动方法一样，每次调用InterceptHandler的notifyTopicPublished方法都是在线程池中新建一个任务

具体代码：

public class PublishTask implements Runnable {
        final MqttPublishMessage msg;
        final InterceptHandler interceptHandler;
        final String clientId;
        final String username;

        PublishTask(MqttPublishMessage msg, InterceptHandler interceptHandler, String clientId, String username) {
            this.msg = msg;
            this.interceptHandler = interceptHandler;
            this.clientId = clientId;
            this.username = username;
        }

        @Override
        public void run() {
            try {
                interceptHandler.onPublish(new InterceptPublishMessage(msg, clientId, username));
            } finally {
                ReferenceCountUtil.release(msg);
            }
        }

        @Override
        public String toString() {
            return "PublishTask{" +
                    "msg=" + msg +
                    ", interceptHandler=" + interceptHandler +
                    ", clientId='" + clientId + '\'' +
                    ", username='" + username + '\'' +
                    '}';
        }

        public InterceptHandler getInterceptHandler() {
            return interceptHandler;
        }
    }


    @Override
    public void notifyTopicPublished(final MqttPublishMessage msg, final String clientID, final String username) {

        msg.retain();

        try {
            for (InterceptHandler handler : handlers.get(InterceptPublishMessage.class)) {
                executor.execute(new PublishTask(msg.retainedDuplicate(), handler, clientID, username));
            }
        } finally {
            ReferenceCountUtil.release(msg);
        }


//        executor.execute(() -> {
//                try {
//                    int messageId = msg.variableHeader().messageId();
//                    String topic = msg.variableHeader().topicName();
//                    for (InterceptHandler handler : handlers.get(InterceptPublishMessage.class)) {
//                        LOG.debug("Notifying MQTT PUBLISH message to interceptor. CId={}, messageId={}, topic={}, "
//                                + "interceptorId={}", clientID, messageId, topic, handler.getID());
//                        handler.onPublish(new InterceptPublishMessage(msg, clientID, username));
//                    }
//                } finally {
//                    ReferenceCountUtil.release(msg);
//                }
//        });
    }

解释：
（1）新建一个PublishTask用来实现调用handler.onPublish()方法。其中要注意
new PublishTask(msg.retainedDuplicate(), handler, clientID, username)中的msg.retainedDuplicate()
还要主要在两个finally中ReferenceCountUtil.release(msg);

（2）PublishTask的toString()和getInterceptHandler()可以先不用管，会在其它地方用到，下一篇文章会讲到。
moquette改造笔记(三)：优化BrokerInterceptor 中的线程池