Provided by: libzmq-dev_2.2.0+dfsg-7_amd64 
NAME
zmq_device - start built-in 0MQ device
SYNOPSIS
int zmq_device (int device, const void *frontend, const void *backend);
DESCRIPTION
The zmq_device() function starts a built-in 0MQ device. The device argument is one of:
ZMQ_QUEUE
starts a queue device
ZMQ_FORWARDER
starts a forwarder device
ZMQ_STREAMER
starts a streamer device
The device connects a frontend socket to a backend socket. Conceptually, data flows from frontend to
backend. Depending on the socket types, replies may flow in the opposite direction.
Before calling zmq_device() you must set any socket options, and connect or bind both frontend and
backend sockets. The two conventional device models are:
proxy
bind frontend socket to an endpoint, and connect backend socket to downstream components. A proxy
device model does not require changes to the downstream topology but that topology is static (any
changes require reconfiguring the device).
broker
bind frontend socket to one endpoint and bind backend socket to a second endpoint. Downstream
components must now connect into the device. A broker device model allows a dynamic downstream
topology (components can come and go at any time).
zmq_device() runs in the current thread and returns only if/when the current context is closed.
QUEUE DEVICE
ZMQ_QUEUE creates a shared queue that collects requests from a set of clients, and distributes these
fairly among a set of services. Requests are fair-queued from frontend connections and load-balanced
between backend connections. Replies automatically return to the client that made the original request.
This device is part of the request-reply pattern. The frontend speaks to clients and the backend speaks
to services. You should use ZMQ_QUEUE with a ZMQ_XREP socket for the frontend and a ZMQ_XREQ socket for
the backend. Other combinations are not documented.
Refer to zmq_socket(3) for a description of these socket types.
FORWARDER DEVICE
ZMQ_FORWARDER collects messages from a set of publishers and forwards these to a set of subscribers. You
will generally use this to bridge networks, e.g. read on TCP unicast and forward on multicast.
This device is part of the publish-subscribe pattern. The frontend speaks to publishers and the backend
speaks to subscribers. You should use ZMQ_FORWARDER with a ZMQ_SUB socket for the frontend and a ZMQ_PUB
socket for the backend. Other combinations are not documented.
Refer to zmq_socket(3) for a description of these socket types.
STREAMER DEVICE
ZMQ_STREAMER collects tasks from a set of pushers and forwards these to a set of pullers. You will
generally use this to bridge networks. Messages are fair-queued from pushers and load-balanced to
pullers.
This device is part of the pipeline pattern. The frontend speaks to pushers and the backend speaks to
pullers. You should use ZMQ_STREAMER with a ZMQ_PULL socket for the frontend and a ZMQ_PUSH socket for
the backend. Other combinations are not documented.
Refer to zmq_socket(3) for a description of these socket types.
RETURN VALUE
The zmq_device() function always returns -1 and errno set to ETERM (the 0MQ context associated with
either of the specified sockets was terminated).
EXAMPLE
Creating a queue broker.
// Create frontend and backend sockets
void *frontend = zmq_socket (context, ZMQ_XREP);
assert (backend);
void *backend = zmq_socket (context, ZMQ_XREQ);
assert (frontend);
// Bind both sockets to TCP ports
assert (zmq_bind (frontend, "tcp://*:5555") == 0);
assert (zmq_bind (backend, "tcp://*:5556") == 0);
// Start a queue device
zmq_device (ZMQ_QUEUE, frontend, backend);
SEE ALSO
zmq_bind(3) zmq_connect(3) zmq_socket(3) zmq(7)
AUTHORS
This manual page was written by the 0MQ community.