ØMQ Manual - ØMQ/4.1.7


zmq_proxy_steerable - built-in ØMQ proxy with control flow


int zmq_proxy_steerable (const void *frontend, const void *backend, const void *capture, const void *control);


The zmq_proxy_steerable() function starts the built-in ØMQ proxy in the current application thread, as zmq_proxy() do. Please, refer to this function for the general description and usage. We describe here only the additional control flow provided by the socket passed as the fourth argument "control".

If the control socket is not NULL, the proxy supports control flow. If PAUSE is received on this socket, the proxy suspends its activities. If RESUME is received, it goes on. If TERMINATE is received, it terminates smoothly. At start, the proxy runs normally as if zmq_proxy was used.

If the control socket is NULL, the function behave exactly as if zmq_proxy had been called.

Refer to zmq_socket(3) for a description of the available socket types. Refer to zmq_proxy(3) for a description of the zmq_proxy.

Example usage

cf zmq_proxy

Return value

The zmq_proxy_steerable() function returns 0 if TERMINATE is sent to its control socket. Otherwise, it returns -1 and errno set to ETERM (the ØMQ context associated with either of the specified sockets was terminated).


Creating a shared queue proxy

// Create frontend, backend and control sockets
void *frontend = zmq_socket (context, ZMQ_ROUTER);
assert (backend);
void *backend = zmq_socket (context, ZMQ_DEALER);
assert (frontend);
void *control = zmq_socket (context, ZMQ_SUB);
assert (control);

// Bind sockets to TCP ports
assert (zmq_bind (frontend, "tcp://*:5555") == 0);
assert (zmq_bind (backend, "tcp://*:5556") == 0);
assert (zmq_connect (control, "tcp://*:5557") == 0);

// Subscribe to the control socket since we have chosen SUB here
assert (zmq_setsockopt (control, ZMQ_SUBSCRIBE, "", 0));

// Start the queue proxy, which runs until ETERM or "TERMINATE"
// received on the control socket zmq_proxy_steerable (frontend, backend, NULL, control);

Set up a controller in another node, process or whatever

void *control = zmq_socket (context, ZMQ_PUB);
assert (control);
assert (zmq_bind (control, "tcp://*:5557") == 0);

// pause the proxy
assert (zmq_send (control, "PAUSE", 5, 0) == 0);

// resume the proxy
assert (zmq_send (control, "RESUME", 6, 0) == 0);

// terminate the proxy
assert (zmq_send (control, "TERMINATE", 9, 0) == 0);


zmq_proxy(3) zmq_bind(3) zmq_connect(3) zmq_socket(3) zmq(7)


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