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.