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我对带有本地 C++ CMS 客户端 3.9.3 的 ActiveMQ 5.11 代理有疑问。我修改了官方网站上的示例代码，使用 pthread_create 函数生成一个新线程并尝试从新线程确认消息（CLIENT_ACK 模式）。事实证明存在分段错误。我们如何实现从新生成的线程而不是当前线程返回 ack？ActiveMQ C++ 客户端是否支持多线程确认消息？

void* sendAckThreadFunc(void *pMessage) {
    sleep(1);
    const Message* message = (const Message*) pMessage;
    message->acknowledge();
    printf("ACK sent out.");        
    return NULL;
}



   virtual void onMessage(const Message* message) {

        static int count = 0;

        try {
            count++;
            const TextMessage* textMessage = dynamic_cast<const TextMessage*>(message);
            string text = "";

            if (textMessage != NULL) {
                text = textMessage->getText();
            } else {
                text = "NOT A TEXTMESSAGE!";
            }


            if (clientAck) {

                //message->acknowledge();  --> instead of ack the message in the onMessage function, they use pthread_create to generate a new thread and trying to ack the message from there. Is is a supported way??
                pthread_t sendAckThread;                
                if (pthread_create(&sendAckThread, NULL, sendAckThreadFunc,
                    (void*) message)) {
                    printf("Error occured when create threads.");
                }
            }

            printf("A Message #%d Received: %s\n", count, text.c_str());
        } catch (CMSException& e) {
            e.printStackTrace();
        }
    }

当我运行消费者时，它甚至无法尝试确认一条消息：

[root@amq6-283-1 examples]# ./simple_async_consumer
=====================================================
Starting the example:
-----------------------------------------------------
The Connection's Transport has been Restored.
Press 'q' to quit
A Message #1 Received: Hello world! from thread 140486368756208
Segmentation fault (core dumped)

这里的事情是，一旦消息对象退出 OnMessage 函数，所有的资源都没有了，无法传递给其他线程。

CMS API 文档清楚地说明了这一点：

        /**
         * Called asynchronously when a new message is received, the message
         * reference can be to any of the Message types. a dynamic cast is used
         * to find out what type of message this is.  The lifetime of this
         * object is only guaranteed to be for the life of the onMessage function
         * after this call-back returns the message may no longer exist. Users should
         * copy the data or clone the message if they wish to retain information that
         * was contained in this Message.
         *
         * It is considered a programming error for this method to throw an
         * exception.  The method has been tagged with the 'throw()' qualifier,
         * this implies that you application will segfault if you throw an error
         * from an implementation of this method.
         *
         * @param message
         *      Message object {const} pointer recipient does not own.
         */

我了解示例仅用于串行处理，但我真诚地要求进行并行处理，这意味着所有事情都不是在单个线程中完成的。如果是串行的，在当前消息被处理并返回 ack 之前，当前线程无法接收更多批次的消息。确实不能满足客户的性能需求。

那么任何人都可以说明 CMS API 是如何设计来处理并行性的吗？Receiver 线程只专注于接收OnMessage函数内部的消息，而其他业务线程则专注于业务处理并根据结果返回 ack。我只想知道 CMS API 如何处理并行性。这就是他们使用 CLIENT ACK 模式的方式。任何人都可以提供一个并行示例吗？

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1 回答 1

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不确定“ onMessage ” API 文档的哪一部分在这里不清楚，但为了帮助，我将其粘贴在这里：

    /**
     * Called asynchronously when a new message is received, the message
     * reference can be to any of the Message types. a dynamic cast is used
     * to find out what type of message this is.  The lifetime of this
     * object is only guaranteed to be for life of the onMessage function
     * after this call-back returns the message may no longer exist.  Users should
     * copy the data or clone the message if they wish to retain information that
     * was contained in this Message.
     *
     * It is considered a programming error for this method to throw an
     * exception.  The method has been tagged with the 'throw()' qualifier,
     * this implies that you application will segfault if you throw an error
     * from an implementation of this method.
     *
     * @param message
     *      Message object {const} pointer recipient does not own.
     */
    virtual void onMessage(const Message* message) = 0;

因此，阅读后似乎很清楚，如果您想存储消息以供以后确认，您需要使用内置的消息对象“克隆”API 克隆它。

于 2019-11-12T14:44:54.147 回答