CODEWITHSUNDEEP
pythonc++zeromqc++20
NoA
NoA

Reputation: 23

ZeroMQ - C++ Publisher and Python Subscriber

I am unable to receive messages sent via ZeroMQ by a C++ publisher with a Python subscriber. Messages sent via Python publisher can be received by a Python subscriber but those sent through a C++ publisher can't.

Here's some more details and simplified code.

Python Subscriber

import zmq
import time

if __name__ == '__main__':

    context = zmq.Context()
    socket = context.socket(zmq.SUB)
    socket.bind("tcp://127.0.0.1:98765")
    socket.setsockopt_string(zmq.SUBSCRIBE, "")

    while True:
        print(socket.recv())
        time.sleep(1)

C++ Publisher (not working)

#include <string>
#include <zmq.hpp>
#include <unistd.h>

using std::string;

int main() {

    zmq::context_t context(1);
    zmq::socket_t socket(context, ZMQ_PUB);
    socket.connect("tcp://127.0.0.1:98765");

    string pub_msg = "greetings from C++";
    zmq::message_t message_to_send(pub_msg.size());
    memcpy(message_to_send.data(), pub_msg.c_str(), pub_msg.size());
    socket.send(message_to_send, zmq::send_flags::dontwait);
    usleep(10*1000000);

}

Python Publisher (working)

import zmq
import time

if __name__ == '__main__':

    context = zmq.Context()
    socket = context.socket(zmq.PUB)
    socket.connect("tcp://127.0.0.1:98765")

    while True:
        socket.send("greetings from Python")
        time.sleep(1)

I want to have the Python subscriber working with C++ publisher. I have tried binding the C++ publisher and connecting Python subscriber but that also doesn't work.

Some direction here would be very helpful.

Thanks Noman.

Upvotes: 0

Views: 862

Answers (2)

jamesdillonharvey
jamesdillonharvey

Reputation: 1042

Regarding the C++ ZMQ_PUB version, its possible the message is being sent before the connect() establishes a connection as its async.

PUB will throw the message away if the connection is not established, PUSH on the other hand will queue.

Try adding a sleep between connect and send

Upvotes: 0

NoA
NoA

Reputation: 23

So, it turns out changing

Python

socket = context.socket(zmq.PULL)  # from context.socket(zmq.SUB)

C++

zmq::socket_t socket(context, ZMQ_PUSH);  // from socket(context, ZMQ_PUB)

helped fix my problem.

I don't have an explanation for it, but for my use-case, this should do.

Upvotes: 0

Related Questions