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authorMartin Sustrik <sustrik@250bpm.com>2012-02-16 10:01:47 +0900
committerMartin Sustrik <sustrik@250bpm.com>2012-02-16 10:01:47 +0900
commit4a7aad06d95701cf232198093ce396dcdbb53e5b (patch)
tree8ced8929e603a179d9434099244dfd782e705d5e /doc/zmq_socket.txt
parent1fc63e4dbcf1438eb571d720f57be68852f820f7 (diff)
ZeroMQ renamed to Crossroads
Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
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-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 newly created socket is initially unbound, and not associated with any
-endpoints. In order to establish a message flow a socket must first be
-connected to at least one endpoint with linkzmq:zmq_connect[3], or at least one
-endpoint must be created for accepting incoming connections with
-linkzmq:zmq_bind[3].
-
-.Key differences to conventional sockets
-Generally speaking, conventional sockets present a _synchronous_ interface to
-either connection-oriented reliable byte streams (SOCK_STREAM), or
-connection-less unreliable datagrams (SOCK_DGRAM). In comparison, 0MQ sockets
-present an abstraction of an asynchronous _message queue_, with the exact
-queueing semantics depending on the socket type in use. Where conventional
-sockets transfer streams of bytes or discrete datagrams, 0MQ sockets transfer
-discrete _messages_.
-
-0MQ sockets being _asynchronous_ means that the timings of the physical
-connection setup and tear down, reconnect and effective delivery are transparent
-to the user and organized by 0MQ itself. Further, messages may be _queued_ in
-the event that a peer is unavailable to receive them.
-
-Conventional sockets allow only strict one-to-one (two peers), many-to-one
-(many clients, one server), or in some cases one-to-many (multicast)
-relationships. With the exception of 'ZMQ_PAIR', 0MQ sockets may be connected
-*to multiple endpoints* using _zmq_connect()_, while simultaneously accepting
-incoming connections *from multiple endpoints* bound to the socket using
-_zmq_bind()_, thus allowing many-to-many relationships.
-
-.Thread safety
-0MQ 'sockets' are _not_ thread safe. Applications MUST NOT use a socket
-from multiple threads except after migrating a socket from one thread to
-another with a "full fence" memory barrier.
-
-.Socket types
-0MQ defines several messaging patterns which encapsulate exact semantics of
-a particular topology. For example, publush-subscribe pattern defines data
-distribution trees while request-reply defines networks of shared stateless
-services. Each pattern defines several socket types (roles in the pattern).
-
-The following sections present the socket types defined by 0MQ:
-
-
-Request-reply pattern
-~~~~~~~~~~~~~~~~~~~~~
-The request-reply pattern is used for sending requests from a _client_ to one
-or more instances of a stateless _service_, and receiving subsequent replies
-to each request sent.
-
-
-ZMQ_REQ
-^^^^^^^
-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 _services_, and each reply received is
-matched with the last issued request.
-
-When a 'ZMQ_REQ' socket enters an exceptional state due to having reached the
-high water mark for all _services_, or if there are no _services_ at all, then
-any linkzmq:zmq_send[3] operations on the socket shall block until the
-exceptional state ends or at least one _service_ becomes available for sending;
-messages are not discarded.
-
-[horizontal]
-.Summary of ZMQ_REQ characteristics
-Compatible peer sockets:: 'ZMQ_REP'
-Send/receive pattern:: Send, Receive, Send, Receive, ...
-Outgoing routing strategy:: Load-balanced
-Incoming routing strategy:: Last peer
-ZMQ_HWM option action:: Block
-
-
-ZMQ_REP
-^^^^^^^
-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
-request received is fair-queued from among all _clients_, and each reply sent
-is routed to the _client_ that issued the last request. If the original
-requester doesn't exist any more the reply is silently discarded.
-
-When a 'ZMQ_REP' socket enters an exceptional state due to having reached the
-high water mark for a _client_, then any replies sent to the _client_ in
-question shall be dropped until the exceptional state ends.
-
-[horizontal]
-.Summary of ZMQ_REP characteristics
-Compatible peer sockets:: 'ZMQ_REQ'
-Send/receive pattern:: Receive, Send, Receive, Send, ...
-Incoming routing strategy:: Fair-queued
-Outgoing routing strategy:: Last peer
-ZMQ_HWM option action:: Drop
-
-
-ZMQ_XREQ
-^^^^^^^^
-A socket of type 'ZMQ_XREQ' is a socket type underlying 'ZMQ_REQ'. It doesn't
-impose the strict order of sends and recvs as 'ZMQ_REQ' does and it is
-intended for use in intermediate devices in request-reply topologies.
-
-Each message sent is load-balanced among all connected
-peers, and each message received is fair-queued from all connected peers.
-
-When a 'ZMQ_XREQ' socket enters an exceptional state due to having reached the
-high water mark for all peers, or if there are no peers at all, then any
-linkzmq:zmq_send[3] operations on the socket shall block until the exceptional
-state ends or at least one peer becomes available for sending; messages are not
-discarded.
-
-[horizontal]
-.Summary of ZMQ_XREQ characteristics
-Compatible peer sockets:: 'ZMQ_XREP', 'ZMQ_REP'
-Send/receive pattern:: Unrestricted
-Outgoing routing strategy:: Load-balanced
-Incoming routing strategy:: Fair-queued
-ZMQ_HWM option action:: Block
-
-
-ZMQ_XREP
-^^^^^^^^
-A socket of type 'ZMQ_XREP' is a socket type underlying 'ZMQ_REP'. It doesn't
-impose the strict order of sends and recvs as 'ZMQ_REQ' does and it is
-intended for use in intermediate devices in request-reply topologies.
-
-Messages received are fair-queued from among all connected peers. The outbound
-messages are routed to a specific peer, as explained below.
-
-When a 'ZMQ_XREP' socket enters an exceptional state due to having reached the
-high water mark for all peers, or if there are no peers at all, then any
-messages sent to the socket shall be dropped until the exceptional state ends.
-Likewise, any messages to be routed to a non-existent peer or a peer for which
-the individual high water mark has been reached shall also be dropped.
-
-[horizontal]
-.Summary of ZMQ_XREP characteristics
-Compatible peer sockets:: 'ZMQ_XREQ', 'ZMQ_REQ'
-Send/receive pattern:: Unrestricted
-Outgoing routing strategy:: See text
-Incoming routing strategy:: Fair-queued
-ZMQ_HWM option action:: Drop
-
-
-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 fan out fashion.
-
-
-ZMQ_PUB
-^^^^^^^
-A socket of type 'ZMQ_PUB' is used by a _publisher_ to distribute data.
-Messages sent are distributed in a fan out fashion to all connected peers.
-The linkzmq:zmq_recv[3] function is not implemented for this socket type.
-
-When a 'ZMQ_PUB' socket enters an exceptional state due to having reached the
-high water mark for a _subscriber_, then any messages that would be sent to the
-_subscriber_ in question shall instead be dropped until the exceptional state
-ends. The _zmq_send()_ function shall never block for this socket type.
-
-[horizontal]
-.Summary of ZMQ_PUB characteristics
-Compatible peer sockets:: 'ZMQ_SUB', 'ZMQ_XSUB'
-Send/receive pattern:: Send only
-Incoming routing strategy:: N/A
-Outgoing routing strategy:: Fan out
-ZMQ_HWM option action:: Drop
-
-
-ZMQ_SUB
-^^^^^^^
-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 linkzmq:zmq_setsockopt[3] to
-specify which messages to subscribe to. The _zmq_send()_ function is not
-implemented for this socket type.
-
-[horizontal]
-.Summary of ZMQ_SUB characteristics
-Compatible peer sockets:: 'ZMQ_PUB', 'ZMQ_XPUB'
-Send/receive pattern:: Receive only
-Incoming routing strategy:: Fair-queued
-Outgoing routing strategy:: N/A
-ZMQ_HWM option action:: Drop
-
-
-ZMQ_XPUB
-^^^^^^^^
-Same as ZMQ_PUB except that you can receive subscriptions from the peers
-in form of incoming messages. Subscription message is a byte 1 (for
-subscriptions) or byte 0 (for unsubscriptions) followed by the subscription
-body.
-
-[horizontal]
-.Summary of ZMQ_XPUB characteristics
-Compatible peer sockets:: 'ZMQ_SUB', 'ZMQ_XSUB'
-Send/receive pattern:: Send messages, receive subscriptions
-Incoming routing strategy:: N/A
-Outgoing routing strategy:: Fan out
-ZMQ_HWM option action:: Drop
-
-
-ZMQ_XSUB
-^^^^^^^^
-Same as ZMQ_SUB except that you subscribe by sending subscription messages to
-the socket. Subscription message is a byte 1 (for subscriptions) or byte 0
-(for unsubscriptions) followed by the subscription body.
-
-[horizontal]
-.Summary of ZMQ_XSUB characteristics
-Compatible peer sockets:: 'ZMQ_PUB', 'ZMQ_XPUB'
-Send/receive pattern:: Receive messages, send subscriptions
-Incoming routing strategy:: Fair-queued
-Outgoing routing strategy:: N/A
-ZMQ_HWM option action:: Drop
-
-
-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 load-balanced among all connected _nodes_.
-
-
-ZMQ_PUSH
-^^^^^^^^
-A socket of type 'ZMQ_PUSH' 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.
-
-When a 'ZMQ_PUSH' socket enters an exceptional state due to having reached the
-high water mark for all downstream _nodes_, or if there are no downstream
-_nodes_ at all, then any linkzmq:zmq_send[3] operations on the socket shall
-block until the exceptional state ends or at least one downstream _node_
-becomes available for sending; messages are not discarded.
-
-[horizontal]
-.Summary of ZMQ_PUSH characteristics
-Compatible peer sockets:: 'ZMQ_PULL'
-Direction:: Unidirectional
-Send/receive pattern:: Send only
-Incoming routing strategy:: N/A
-Outgoing routing strategy:: Load-balanced
-ZMQ_HWM option action:: Block
-
-
-ZMQ_PULL
-^^^^^^^^
-A socket of type 'ZMQ_PULL' 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.
-
-[horizontal]
-.Summary of ZMQ_PULL characteristics
-Compatible peer sockets:: 'ZMQ_PUSH'
-Direction:: Unidirectional
-Send/receive pattern:: Receive only
-Incoming routing strategy:: Fair-queued
-Outgoing routing strategy:: N/A
-ZMQ_HWM option action:: N/A
-
-
-Exclusive pair pattern
-~~~~~~~~~~~~~~~~~~~~~~
-The exclusive pair is an advanced pattern used for communicating exclusively
-between two peers.
-
-
-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.
-
-When a 'ZMQ_PAIR' socket enters an exceptional state due to having reached the
-high water mark for the connected peer, or if no peer is connected, then
-any linkzmq:zmq_send[3] operations on the socket shall block until the peer
-becomes available for sending; messages are not discarded.
-
-NOTE: 'ZMQ_PAIR' sockets are experimental, and are currently missing several
-features such as auto-reconnection.
-
-[horizontal]
-.Summary of ZMQ_PAIR characteristics
-Compatible peer sockets:: 'ZMQ_PAIR'
-Direction:: Bidirectional
-Send/receive pattern:: Unrestricted
-Incoming routing strategy:: N/A
-Outgoing routing strategy:: N/A
-ZMQ_HWM option action:: Block
-
-
-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.
-*EFAULT*::
-The provided 'context' is invalid.
-*EMFILE*::
-The limit on the total number of open 0MQ sockets has been reached.
-*ETERM*::
-The context specified was terminated.
-
-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]
-linkzmq:zmq[7]
-
-
-AUTHORS
--------
-The 0MQ documentation was written by Martin Sustrik <sustrik@250bpm.com> and
-Martin Lucina <martin@lucina.net>.