[zeromq-dev] Question about zmq_socket_monitor()

[Martin.Belanger at dell.com]

Hi,

I'm experimenting with ​zmq_socket_monitor(). I have a XSUB socket that I'm monitoring. The monitoring works fine. I'm just trying to understand how I can enable/disable monitoring back-and-forth by calling zmq_socket_monitor().

I tried to enable/disable/re-enable monitoring by invoking zmq_socket_monitor() as shown below I get the error "Address already in use" on the 3rd invocation.

1) zmq_socket_monitor(my_xsub_sock, "inproc://starship-enterprise", ZMQ_EVENT_ALL);
2) zmq_socket_monitor(my_xsub_sock, NULL, 0);
3) zmq_socket_monitor(my_xsub_sock, "inproc://starship-enterprise", ZMQ_EVENT_ALL); <- ERROR

I followed the source code for zmq_socket_monitor() to a method called zmq::socket_base_t::monitor(). That function eventually calls zmq_bind() where I believe the error occurs. 

1) The first time zmq_socket_monitor() is called a ZMQ_PAIR socket is created (_monitor_socket) and bound to address "inproc://starship-enterprise". Note that this socket is created with ZMQ_LINGER=0.

2) The second time zmq_socket_monitor() is invoked to disable monitoring _monitor_socket is closed and because ZMQ_LINGER=0 it should go out of existence right away. Right?

3) The third time zmq_socket_monitor() is called I get "Address already in use" as if the old socket is still there. How can that be?

Regards,
Martin