消息队列zmq常用通信模式

zmq是一个消息队列。可以在进程内、进程间、TCP、多播中，以消息为单位传输数据，而不是socket的字节流。官方主页上有下载、使用、文档，蛮全的。

常用模式有：Request-Reply，Publish-Subscribe，Parallel Pipeline。

Request-Reply

request

zmq::context_t context (1);
zmq::socket_t socket (context, ZMQ_REQ);
//Send the request
zmq::message_t request(6);
memcpy ((void *)request.data(), "Hello", 5);
socket.send(request);
//Get the reply
zmq::message_t reply;
socket.recv(&reply);

server

zmq::context_t context (1);
zmq::socket_t socket(context, ZMQ_REP);
socket.bind ("tcp://*:5555");
while (true) {
  zmq::message_t request;
  //  Wait for next request from client
  socket.recv (&request);
  std::cout << "Received Hello" << std::endl;
  //  Do some 'work'
  sleep (1);
  //  Send reply back to client
  zmq::message_t reply (5);
  memcpy ((void *) reply.data (), "World", 5);
  socket.send (reply);
}

Publish-Subscribe

publisher

zmq::context_t context (1);
zmq::socket_t publisher (context, ZMQ_PUB);
publisher.bind("tcp://*:5556");
publisher.send(message);

subscriber

zmq::context_t context (1);
zmq::socket_t subscriber (context, ZMQ_SUB);
subscriber.connect("tcp://localhost:5556");
const char *filter = "";
subscriber.setsockopt(ZMQ_SUBSCRIBE, filter, strlen (filter));
zmq::message_t update;
subscriber.recv(&update);

Parallel Pipeline

ventilator

zmq::context_t context (1);
//  Socket to send messages on
zmq::socket_t  sender(context, ZMQ_PUSH);
sender.bind("tcp://*:5557");
//  通知sink开始处理任务
zmq::socket_t sink(context, ZMQ_PUSH);
sink.connect("tcp://localhost:5558");
zmq::message_t message(2);
memcpy(message.data(), "0", 1);
sink.send(message);
//开始往pipeline发送数据
message.rebuild(10);
sprintf ((char *) message.data(), "%d", workload);
sender.send(message);    

worker

zmq::context_t context(1);

//  Socket to receive messages on
zmq::socket_t receiver(context, ZMQ_PULL);
receiver.connect("tcp://localhost:5557");

//  Socket to send messages to
zmq::socket_t sender(context, ZMQ_PUSH);
sender.connect("tcp://localhost:5558");

//  Process tasks forever
while (1) {
  receiver.recv(&message);
  //  Send results to sink
  message.rebuild();
  sender.send(message);
}

sink

//  Prepare our context and socket
zmq::context_t context(1);
zmq::socket_t receiver(context,ZMQ_PULL);
receiver.bind("tcp://*:5558");

//  Wait for start of batch
zmq::message_t message;
receiver.recv(&message);
//receive from worker
receiver.recv(&message);