ZMQ Publish/Subscribe pattern publisher connects to subscribers

Question

I am new to ZMQ and already did the tutorials about the publish subscribe pattern. But for my application they don't quite apply. I have two types of applications. Application one can create connections to multiple "Applications two"s over network and send them data.

I tried implementing this with the Publish/Subscribe pattern, but instead of the subscriber connecting to the publisher the publisher connects to the subscribers.

Publisher:

zmq::context_t context(1);
zmq::socket_t socket(context, ZMQ_PUB);

socket.connect("tcp://localhost:5555");

std::string text = "Hello World";
zmq::message_t message(text.size());
memcpy(message.data(), text.c_str(), text.size());

socket.send(message);

Subscriber:

zmq::context_t context(1);
zmq::socket_t socket(context, ZMQ_SUB);

socket.bind("tcp://*:5555");
const char* filter = "Hello ";
socket.setsockopt(ZMQ_SUBSCRIBE, filter, strlen(filter));

zmq::message_t request;
socket.recv(&request);

std::string message = std::string(static_cast<char*>(request.data()), request.size());

std::cout << "Message received!" << std::endl;
std::cout << message << std::endl;

The publisher finnishes without error, but the subscriber is stuck in the recv(). And yes I am starting them in the right order (subscriber first)

Answer 1

I found the solution myself: The problem is, that the publisher send the message, before the subscriber was ready to receive. A simple

zmq_sleep(1) 

before the

socket.send(message); 

did the job.