I am having some problems with inter process communication in ZMQ between several instances of a program
- I am using Linux OS
- I am using zeromq/cppzmq, header-only C++ binding for libzmq
If I run two instances of this application (say on a terminal), I provide one with an argument to be a listener, then providing the other with an argument to be a sender. The listener never receives a message. I have tried TCP and IPC to no avail.
#include <zmq.hpp>
#include <string>
#include <iostream>
int ListenMessage();
int SendMessage(std::string str);
zmq::context_t global_zmq_context(1);
int main(int argc, char* argv[] ) {
std::string str = "Hello World";
if (atoi(argv[1]) == 0) ListenMessage();
else SendMessage(str);
zmq_ctx_destroy(& global_zmq_context);
return 0;
}
int SendMessage(std::string str) {
assert(global_zmq_context);
std::cout << "Sending \n";
zmq::socket_t publisher(global_zmq_context, ZMQ_PUB);
assert(publisher);
int linger = 0;
int rc = zmq_setsockopt(publisher, ZMQ_LINGER, &linger, sizeof(linger));
assert(rc==0);
rc = zmq_connect(publisher, "tcp://127.0.0.1:4506");
if (rc == -1) {
printf ("E: connect failed: %s\n", strerror (errno));
return -1;
}
zmq::message_t message(static_cast<const void*> (str.data()), str.size());
rc = publisher.send(message);
if (rc == -1) {
printf ("E: send failed: %s\n", strerror (errno));
return -1;
}
return 0;
}
int ListenMessage() {
assert(global_zmq_context);
std::cout << "Listening \n";
zmq::socket_t subscriber(global_zmq_context, ZMQ_SUB);
assert(subscriber);
int rc = zmq_setsockopt(subscriber, ZMQ_SUBSCRIBE, "", 0);
assert(rc==0);
int linger = 0;
rc = zmq_setsockopt(subscriber, ZMQ_LINGER, &linger, sizeof(linger));
assert(rc==0);
rc = zmq_bind(subscriber, "tcp://127.0.0.1:4506");
if (rc == -1) {
printf ("E: bind failed: %s\n", strerror (errno));
return -1;
}
std::vector<zmq::pollitem_t> p = {{subscriber, 0, ZMQ_POLLIN, 0}};
while (true) {
zmq::message_t rx_msg;
// when timeout (the third argument here) is -1,
// then block until ready to receive
std::cout << "Still Listening before poll \n";
zmq::poll(p.data(), 1, -1);
std::cout << "Found an item \n"; // not reaching
if (p[0].revents & ZMQ_POLLIN) {
// received something on the first (only) socket
subscriber.recv(&rx_msg);
std::string rx_str;
rx_str.assign(static_cast<char *>(rx_msg.data()), rx_msg.size());
std::cout << "Received: " << rx_str << std::endl;
}
}
return 0;
}
This code will work if I running one instance of the program with two threads
std::thread t_sub(ListenMessage);
sleep(1); // Slow joiner in ZMQ PUB/SUB pattern
std::thread t_pub(SendMessage str);
t_pub.join();
t_sub.join();
But I am wondering why when running two instances of the program the code above won't work?
Thanks for your help!
