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diff --git a/doc/zmq_device.txt b/doc/zmq_device.txt new file mode 100644 index 0000000..7797693 --- /dev/null +++ b/doc/zmq_device.txt @@ -0,0 +1,92 @@ +zmq_device(3) +============= + +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 linkzmq: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 linkzmq: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 linkzmq: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 +-------- +linkzmq:zmq_bind[3] +linkzmq:zmq_connect[3] +linkzmq:zmq_socket[3] +linkzmq:zmq[7] + |