zeromq - How are multiple message types facilitated through a single connection with 0MQ?

Question

With RabbitMq, subscriptions to multiple queues are achieved over a single connection via Channels. This allows a single socket to be used to process multiple subscriptions. What is the analog strategy for minimizing socket connections for multiple message types in Zero MQ?

Answer 1

我想说 PUB/SUB 消息信封是 ZeroMQ 中解决此问题的首选方法（请参阅Pub-Sub Message Envelopes）。

在发送消息之前，发布者应该在信封中发送其主题：

    s_sendmore (publisher, "A");
    s_send (publisher, <Serialized MessageA>);
    .....
    s_sendmore (publisher, "B");
    s_send (publisher, <Serialized MessageB>);

Suscriber 有 3 个选项来处理多个主题：

• 从信封中读取消息类型，根据消息类型使用反序列化器（图中的客户端 1）。

  char *topic = s_recv (subscriber);
  char *body = s_recv (subscriber);
  //If topic == "A", the body contains serialized MessageA, otherwise MessageB
  

• 使用 仅订阅一个主题zmq_setsockopt (subscriber, ZMQ_SUBSCRIBE, ...);。在这种情况下ZeroMQ会进行PUB端的消息过滤（从3.x开始），客户端可以确定只会接收MessageA类型的消息（图中客户端2）

  char *topic = s_recv (subscriber);
  char *body = s_recv (subscriber);
  //Ignore the topic, the body contains serialized MessageA
  

• 订阅所有消息并在客户端进程中创建一个代理，该代理在INPROC套接字上发布消息。单个订阅者应该使用zmq_setsockopt (subscriber, ZMQ_SUBSCRIBE, ...);订阅单一类型的消息。（见客户 3）。

  void *frontend = zsocket_new (context, ZMQ_SUB);
  zsocket_connect (frontend, "tcp://<....>");
  void *backend = zsocket_new (context, ZMQ_PUB);
  zsocket_bind (backend, "inproc://all_messages");
  //  Start the proxy
  zmq_proxy (frontend, backend, NULL);
  ...
  //On another thread
  void *sub1 = zsocket_new (context, ZMQ_SUB);
  zsocket_connect (sub1, "inproc://all_messages");
  zmq_setsockopt (subscriber, ZMQ_SUBSCRIBE, "A", 1);
  ...
  void *sub2 = zsocket_new (context, ZMQ_SUB);
  zsocket_connect (sub2, "inproc://all_messages");
  zmq_setsockopt (subscriber, ZMQ_SUBSCRIBE, "B", 1);
  

您还可以找到用于各种技巧的有用 XPUB/XSUB 套接字。参见例如 最后值缓存