订阅者上的 ZMQ recv 不遵守设置超时

Question

I am trying to integrate ZMQ communication into a test case but I am having issues with zmq::socket_t::recv essentially blocking indefinitely even though I set a timeout 500ms for the operation. The minimal test case that exhibits the behavior looks like this

#include <gtest/gtest.h>
#include <zmq.hpp>

TEST(timeout, not_working_in_recv)
{
  zmq::context_t zmq_context;
  zmq::socket_t  sub(zmq_context, ZMQ_SUB);

  sub.setsockopt(ZMQ_SUBSCRIBE, nullptr, 0);
  int const timeout_ms = 500;
  sub.setsockopt(ZMQ_RCVTIMEO, &timeout_ms);
  sub.connect("inproc://pubsub_test");

  zmq::message_t msg;
  sub.recv(&msg);
}

There have been more elaborate setups where I set up a thread that creates a corresponding publisher, but the result was always a blocking receive. The block is not quite indefinite, eventually it does actually return.

This is compiled and executed under Windows 10, x32 using MSVC 2017 and ZMQ 4.2.2.

Does anyone know why the receive call is blocking and how this can be fixed?

Answer 1

The timeout is set incorrectly. The line

sub.setsockopt(ZMQ_RCVTIMEO, &timeout_ms); // set timeout to address of timeout_ms variable

should be

sub.setsockopt(ZMQ_RCVTIMEO, timeout_ms); // set timeout to value of timeout_ms