zmq_socket(3) ============= NAME ---- zmq_socket - create 0MQ socket SYNOPSIS -------- *void *zmq_socket (void '*context', int 'type');* DESCRIPTION ----------- The 'zmq_socket()' function shall create a 0MQ socket within the specified 'context' and return an opaque handle to the newly created socket. The 'type' argument specifies the socket type, which determines the semantics of communication over the socket. The following sections present the socket types defined by 0MQ, grouped by the general _messaging pattern_ built from related socket types. Request-reply pattern ~~~~~~~~~~~~~~~~~~~~~ The request-reply pattern is used for sending requests from a _client_ to a _service_, and receiving subsequent replies to each request sent. Socket type:: 'ZMQ_REQ' Compatible peer sockets:: 'ZMQ_REP' A socket of type 'ZMQ_REQ' is used by a _client_ to send requests to and receive replies from a _service_. This socket type allows only an alternating sequence of _zmq_send(request)_ and subsequent _zmq_recv(reply)_ calls. Each request sent is load-balanced among all connected _services_. Socket type:: 'ZMQ_REP' Compatible peer sockets:: 'ZMQ_REQ' A socket of type 'ZMQ_REP' is used by a _service_ to receive requests from and send replies to a _client_. This socket type allows only an alternating sequence of _zmq_recv(request)_ and subsequent _zmq_send(reply)_ calls. Each reply is routed to the _client_ that issued the last received request. Publish-subscribe pattern ~~~~~~~~~~~~~~~~~~~~~~~~~ The publish-subscribe pattern is used for one-to-many distribution of data from a single _publisher_ to multiple _subscribers_ in a fanout fashion. Socket type:: 'ZMQ_PUB' Compatible peer sockets:: 'ZMQ_SUB' A socket of type 'ZMQ_PUB' is used by a _publisher_ to distribute data. Messages sent are distributed in a fanout fashion to all connected peers. The _zmq_recv()_ function is not implemented for this socket type. Socket type:: 'ZMQ_SUB' Compatible peer sockets:: 'ZMQ_PUB' A socket of type 'ZMQ_SUB' is used by a _subscriber_ to subscribe to data distributed by a _publisher_. Initially a 'ZMQ_SUB' socket is not subscribed to any messages, use the 'ZMQ_SUBSCRIBE' option of _zmq_setsockopt()_ to specify which messages to subscribe to. The _zmq_send()_ function is not implemented for this socket type. Pipeline pattern ~~~~~~~~~~~~~~~~ The pipeline pattern is used for distributing data to _nodes_ arranged in a pipeline. Data always flows *down* the pipeline, and each stage of the pipeline is connected to at least one _node_. When a pipeline stage is connected to multiple _nodes_ data is processed by all connected _nodes_ in parallel. Socket type:: 'ZMQ_DOWNSTREAM' Compatible peer sockets:: 'ZMQ_UPSTREAM' A socket of type 'ZMQ_DOWNSTREAM' is used by a pipeline _node_ to send messages to downstream pipeline _nodes_. Messages are load-balanced to all connected downstream _nodes_. The _zmq_recv()_ function is not implemented for this socket type. Socket type:: 'ZMQ_UPSTREAM' Compatible peer sockets:: 'ZMQ_DOWNSTREAM' A socket of type 'ZMQ_UPSTREAM' is used by a pipeline _node_ to receive messages from upstream pipeline _nodes_. Messages are fair-queued from among all connected upstream _nodes_. The _zmq_send()_ function is not implemented for this socket type. Exclusive pair pattern ~~~~~~~~~~~~~~~~~~~~~~ The exclusive pair pattern is used for communicating exclusively between two peers. Socket type:: 'ZMQ_PAIR' Compatible peer sockets:: 'ZMQ_PAIR' A socket of type 'ZMQ_PAIR' can only be connected to a single peer at any one time. No message routing or filtering is performed on messages sent over a 'ZMQ_PAIR' socket. NOTE: 'ZMQ_PAIR' sockets are experimental, and are currently missing several features such as auto-reconnection. Developers should consider other patterns in preference to the exclusive pair pattern. RETURN VALUE ------------ The _zmq_socket()_ function shall return an opaque handle to the newly created socket if successful. Otherwise, it shall return NULL and set 'errno' to one of the values defined below. ERRORS ------ *EINVAL*:: The requested socket 'type' is invalid. *EMTHREAD*:: The number of application threads using sockets within this 'context' has been exceeded. See the 'app_threads' parameter of the _zmq_init()_ function. SEE ALSO -------- linkzmq:zmq_init[3] linkzmq:zmq_setsockopt[3] linkzmq:zmq_bind[3] linkzmq:zmq_connect[3] linkzmq:zmq_send[3] linkzmq:zmq_recv[3] AUTHORS ------- The 0MQ documentation was written by Martin Sustrik and Martin Lucina .