ZMQ_REQ socket does not report ZMQ_POLLOUT when ZMQ_REQ_RELAXED is set

[rolftimmermans]

Issue description

When creating a ZMQ_REQ socket with ZMQ_REQ_RELAXED enabled, the ZMQ_EVENTS socket option does not indicate the socket is writable after sending the first message. In spite of that, a call to zmq_send() does in fact succeed without errors (as expected).

Environment

• libzmq version: 4.4.2
• OS: macOS High Sierra

Minimal test code

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

int main() {
    void* ctx = zmq_ctx_new();
    void* req = zmq_socket(ctx, ZMQ_REQ);
    void* rep = zmq_socket(ctx, ZMQ_REP);

    int res;
    int events;
    size_t events_len;

    int relaxed = 1;
    res = zmq_setsockopt(req, ZMQ_REQ_RELAXED, &relaxed, sizeof(relaxed));
    assert(res == 0);

    res = zmq_connect(req, "tcp://127.0.0.1:12345");
    assert(res == 0);

    res = zmq_bind(rep, "tcp://127.0.0.1:12345");
    assert(res == 0);

    sleep(1);

    res = zmq_getsockopt(req, ZMQ_EVENTS, &events, &events_len);
    assert(res == 0);
    printf("%i\n", (events & ZMQ_POLLOUT) == ZMQ_POLLOUT);

    res = zmq_send(req, "foo", 3, 0);
    assert(res == 3);

    res = zmq_getsockopt(req, ZMQ_EVENTS, &events, &events_len);
    assert(res == 0);
    printf("%i\n", (events & ZMQ_POLLOUT) == ZMQ_POLLOUT);

    res = zmq_send(req, "bar", 3, 0);
    assert(res == 3);
    return 0
}

What's the actual result?

The output of this program is:

1
0

That is; (events & ZMQ_POLLOUT) == ZMQ_POLLOUT evaluates as true for the first message, but false after sending the second message.

What's the expected result?

My expectation is that the output would be:

1
1

In other words; (events & ZMQ_POLLOUT) == ZMQ_POLLOUT for the REQ socket if ZMQ_REQ_RELAXED is set.

This seems like a problem in https://github.com/zeromq/libzmq/blob/master/src/req.cpp#L216 – I believe the code should check for strictness just like sending does; therefore I think it should be:

if (receiving_reply && strict)
    return false;

Does this make sense? Am I right in expecting that the REQ socket with ZMQ_REQ_RELAXED enabled should be writable according to the ZMQ_EVENTS socket option?

[bluca]

Yeah I think it makes sense, and your fix should work. Would you please send a PR, including the test for it?

[rolftimmermans]

I would, but I'm struggling to run the tests. Is there any guide?

[rolftimmermans]

Think I managed to get it working on macOS by running:

sudo sysctl -w kern.maxfiles=64000
sudo sysctl -w kern.maxfilesperproc=64000
sudo launchctl limit maxfiles 64000 64000
ulimit -n 64000
rm -rf tmp && BUILD_TYPE=default ./ci_build.sh 

[bluca]

That should work although it's for the CI, make check should be all you need