ZMQ Xpub/Xsub not sending subscription messages - c++11

Question

I am experimenting with ZMQ using a XPUB/XSUB proxy. Ultimately I want to insert some logic in the middle so I attempted to build my own proxy with zmq_poll() instead of using the built in zmq_proxy. However my XPUB never receives any subscription messages to forward. The code below works (subscriber prints "helloWorld" ) if I use the built in proxy. It does not work with my custom proxy. I've tried setting the very verbose/manual socket options and adding delays but can't seem to make it work:
Ex-post [Comment]:
after further testing I realized this was just a dumb copy and past bug and that the arguments to zmq::poll were not what I thought. the second argument is the number of items in the list. which should be 2 and not 1. – CrimsonKnights Dec 13 at 5:45
void proxyBuiltIn(zmq::context_t* context)
{
zmq::socket_t frontend(*context, ZMQ_XSUB);
zmq::socket_t backend(*context, ZMQ_XPUB);
frontend.bind("inproc://frontend");
backend.bind("inproc://backend");
zmq::proxy(frontend, backend);
}
void proxyCustom(zmq::context_t* context)
{
zmq::socket_t frontend(*context, ZMQ_XSUB);
zmq::socket_t backend(*context, ZMQ_XPUB);
frontend.bind("inproc://frontend");
backend.bind("inproc://backend");
zmq::pollitem_t items[2] =
{
{ frontend, 0, ZMQ_POLLIN, 0 },
{ backend, 0, ZMQ_POLLIN, 0 },
};
while (1)
{
if (zmq::poll(items, 1, 1000) == -1){ break;}
if (items[0].revents & ZMQ_POLLIN)
{
std::cout << "got published message" << std::endl; // won't get here because subscription is not made
zmq::multipart_t message;
message.recv(frontend);
message.send(backend);
}
if (items[1].revents & ZMQ_POLLIN)
{
std::cout << "got subscription message" << std::endl; // never gets here.
zmq::multipart_t message;
message.recv(backend);
message.send(frontend);
}
}
}
void subscriber(zmq::context_t* context)
{
zmq::socket_t subscriber(*context, ZMQ_SUB);
subscriber.connect("inproc://backend");
std::string topic = "testTopic";
subscriber.setsockopt(ZMQ_SUBSCRIBE, topic.c_str(), topic.size());
while (1)
{
zmq::multipart_t incoming;
incoming.recv(subscriber);
std::string topic = incoming.popstr();
std::string data = incoming.popstr();
std::cout << topic.c_str() << ", " << data.c_str() << std::endl;
}
}
void publisher(zmq::context_t* context)
{
zmq::socket_t publisher(*context, ZMQ_PUB);
publisher.connect("inproc://frontend");
while (1)
{
zmq::multipart_t message;
message.addstr("testTopic");
message.addstr("helloWorld!");
message.send(publisher);
std::this_thread::sleep_for(std::chrono::milliseconds(1000));
}
}
int main(int argc, char **argv)
{
zmq::context_t* context = new zmq::context_t(1);
std::thread(proxyCustom, context).detach(); // this does not
// std::thread(proxyBuiltIn, context).detach(); // this works
std::thread( publisher, context).detach();
std::thread(subscriber, context).detach();
while(1)
{
}
}