[zeromq-dev] zmq_poll and stdin in C

Bekritsky, Benjamin

2016-12-15 14:47:18 UTC

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-***@lists.zeromq.org] On Behalf Of Bekritsky, Benjamin
Sent: Tuesday, December 13, 2016 5:36 PM
To: zeromq-***@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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