[zeromq-dev] zmq_poll and stdin in C

Bekritsky, Benjamin Benjamin.Bekritsky at zebra.com
Thu Dec 15 15:47:18 CET 2016


I have tested my system (Linux Ubuntu 14.04) and am able to poll for the cli using the native poll command().
I am using ZMQ version 4.2.0.

Here is my code for ZMQ:

#include <zmq.h>
#include <string>
#include <stdio.h>
#include <unistd.h>
#include <string>
#include <iostream>
using namespace std;

int main (void)
{
                cout << "ZMQ CLI Poll Test" << endl;
                int major, minor, patch;
                zmq_version (&major, &minor, &patch);
                cout << "Current ØMQ version is " << major << "." << minor << "." << patch << endl;

                zmq_pollitem_t items [1];
                int rc;
                string request;

    while (1)
    {
                items[0].socket = NULL;
                items[0].fd = STDIN_FILENO;
                items[0].events = ZMQ_POLLIN;
                rc = zmq_poll (items, 1, 1000);
                if (rc < 0)
                {
                                perror("zmq_poll error");
                                return 0;
                }

                if (rc == 0)
                                continue;

                cout << "got something" << endl;
                if (items[0].revents & ZMQ_POLLIN)
                {
                                // Got a request from cli
                                getline(cin, request);
                                cout << request << endl;
}
    }

    return 0;
}

And the very similar code for a standard poll:
#include <poll.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>
#include <iostream>
using namespace std;

int main(void)
{
                cout << "CLI Poll Test" << endl;

                struct pollfd items[1];
                int rc;
                string request;

                while (1)
                {
                                items[0].fd = STDIN_FILENO;
                                items[0].events = POLLIN;
                                rc = poll (items, 1, 1000);

                                if (rc < 0)
                                {
                                                perror("poll error");
                                                return 0;
                                }

                                if (rc == 0)
                                                continue;

                                cout << "got something" << endl;
                                if (items[0].revents & POLLIN)
                                {
                                                // Got a request from cli
                                                getline(cin, request);
                                                cout << request << endl;

                                }

                }

                return 0;
}
Any help would be appreciated.

Thanks,
Benjy
From: zeromq-dev [mailto:zeromq-dev-bounces at lists.zeromq.org] On Behalf Of Bekritsky, Benjamin
Sent: Tuesday, December 13, 2016 5:36 PM
To: zeromq-dev at lists.zeromq.org
Subject: [zeromq-dev] zmq_poll and stdin in C


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I am trying to use zmq_poll on stdin, but find that if something comes in on stdin, the poll returns with a 1, but the .revents field is zero. See code below.

Any subsequent calls to zmq_poll, immediately return with a 1, but .revents field remains 0.

Am I setting up the zmq_pollitem_t properly.

Thanks,
Benjy

int main (void)
{
    void *context = zmq_ctx_new ();

    int rc;
    string request;
    while (1)
    {
                zmq_pollitem_t items [1];
                items[0].socket = NULL;
                items[0].fd = STDIN_FILENO;
                items[0].events = ZMQ_POLLIN;
                /* Poll for events indefinitely */
                rc = zmq_poll (items, 1, -1);

                                if (rc < 0)
                                {
                                                perror("zmq_poll error: ");
                                                return 0;
                                }
                                else if (rc ==0)
                                {
                                                cout << "timeout" << endl;
                                }
                                else
                                {
                                                //cout << rc << endl;
                                                //cout << "items[0].socket: " << items[0].socket <<  " items[0].fd: " <<items[0].fd << " items[0].events: " << items[0].events << " items[0].revents: " <<items[0].revents << endl;
                                                //cout << "items[1].socket: " << items[1].socket <<  " items[1].fd: " <<items[1].fd << " items[1].events: " << items[1].events << " items[1].revents: " <<items[1].revents << endl;

                                }


                                if (items[0].revents & ZMQ_POLLIN)
                                {
                                                // Got a request from cli
                                                getline(cin, request);
                                                cout << request << endl;

                                }
    }
    zmq_ctx_destroy (context);
    return 0;
}


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