Subscription Monitor

To enable an application to republish all its state when a new subscriber connected, we need a way to monitor connection requests. This RFC describes this feature for this use case, based on zmq_socket_monitor.

API

class Sender
{
    virtual void* getSocket() = 0;
};

class Publisher : public Sender {};

class Monitor : public Receiver
{
    Monitor( Sender& sender );
    Monitor( Sender& sender, Receiver& shared );

    virtual void notifyNewConnection() {}
    // other notifies and params lazy, on use case
};

Examples

Livre Communicator derives from Monitor and republishes all events on notify.

Implementation

Publisher socket

Change zeroeq::Publisher socket to ZMQ_XPUB to receive topic subscriptions. Follow the Meerkat pattern to count subscribers.

Other sockets

Monitor installs zmq_socket_monitor() on Sender::getSocket(). Monitor::process() calls Monitor::notifyNewConnection().

Issues

Issue 1: zmq_socket_monitor does not support notifications.

Resolution: Use Meerkat pattern. The initial implementation showed that pub/sub sockets do not support notifications. The Meerkat pattern explains the proper way to do this.