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<body class="manpage">
<div id="header">
<h1>
zmq(7) Manual Page
</h1>
<h2>NAME</h2>
<div class="sectionbody">
<p>zmq -
0MQ lightweight messaging kernel
</p>
</div>
</div>
<div id="content">
<div class="sect1">
<h2 id="_synopsis">SYNOPSIS</h2>
<div class="sectionbody">
<div class="paragraph"><p><strong>#include <zmq.h></strong></p></div>
<div class="paragraph"><p><strong>cc</strong> [<em>flags</em>] <em>files</em> <strong>-lzmq</strong> [<em>libraries</em>]</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph"><p>The ØMQ lightweight messaging kernel is a library which extends the standard
socket interfaces with features traditionally provided by specialised
<em>messaging middleware</em> products. ØMQ sockets provide an abstraction of
asynchronous <em>message queues</em>, multiple <em>messaging patterns</em>, message
filtering (<em>subscriptions</em>), seamless access to multiple <em>transport protocols</em>
and more.</p></div>
<div class="paragraph"><p>This documentation presents an overview of ØMQ concepts, describes how ØMQ
abstracts standard sockets and provides a reference manual for the functions
provided by the ØMQ library.</p></div>
<div class="sect2">
<h3 id="_context">Context</h3>
<div class="paragraph"><p>The ØMQ <em>context</em> keeps the list of sockets and manages the async I/O thread
and internal queries.</p></div>
<div class="paragraph"><p>Before using any ØMQ library functions you must create a ØMQ <em>context</em>. When
you exit your application you must destroy the <em>context</em>. These functions let
you work with <em>contexts</em>:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
Create a new ØMQ context
</dt>
<dd>
<p>
<a href="zmq_ctx_new.html">zmq_ctx_new(3)</a>
</p>
</dd>
<dt class="hdlist1">
Work with context properties
</dt>
<dd>
<p>
<a href="zmq_ctx_set.html">zmq_ctx_set(3)</a>
<a href="zmq_ctx_get.html">zmq_ctx_get(3)</a>
</p>
</dd>
<dt class="hdlist1">
Destroy a ØMQ context
</dt>
<dd>
<p>
<a href="zmq_ctx_shutdown.html">zmq_ctx_shutdown(3)</a>
<a href="zmq_ctx_term.html">zmq_ctx_term(3)</a>
</p>
</dd>
</dl></div>
<div class="sect3">
<h4 id="_thread_safety">Thread safety</h4>
<div class="paragraph"><p>A ØMQ <em>context</em> is thread safe and may be shared among as many application
threads as necessary, without any additional locking required on the part of
the caller.</p></div>
<div class="paragraph"><p>Individual ØMQ <em>sockets</em> are <em>not</em> thread safe except in the case where full
memory barriers are issued when migrating a socket from one thread to another.
In practice this means applications can create a socket in one thread with
<em>zmq_socket()</em> and then pass it to a <em>newly created</em> thread as part of thread
initialisation, for example via a structure passed as an argument to
<em>pthread_create()</em>.</p></div>
</div>
<div class="sect3">
<h4 id="_multiple_contexts">Multiple contexts</h4>
<div class="paragraph"><p>Multiple <em>contexts</em> may coexist within a single application. Thus, an
application can use ØMQ directly and at the same time make use of any number of
additional libraries or components which themselves make use of ØMQ as long as
the above guidelines regarding thread safety are adhered to.</p></div>
</div>
</div>
<div class="sect2">
<h3 id="_messages">Messages</h3>
<div class="paragraph"><p>A ØMQ message is a discrete unit of data passed between applications or
components of the same application. ØMQ messages have no internal structure and
from the point of view of ØMQ itself they are considered to be opaque binary
data.</p></div>
<div class="paragraph"><p>The following functions are provided to work with messages:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
Initialise a message
</dt>
<dd>
<p>
<a href="zmq_msg_init.html">zmq_msg_init(3)</a>
<a href="zmq_msg_init_size.html">zmq_msg_init_size(3)</a>
<a href="zmq_msg_init_data.html">zmq_msg_init_data(3)</a>
</p>
</dd>
<dt class="hdlist1">
Sending and receiving a message
</dt>
<dd>
<p>
<a href="zmq_msg_send.html">zmq_msg_send(3)</a>
<a href="zmq_msg_recv.html">zmq_msg_recv(3)</a>
</p>
</dd>
<dt class="hdlist1">
Release a message
</dt>
<dd>
<p>
<a href="zmq_msg_close.html">zmq_msg_close(3)</a>
</p>
</dd>
<dt class="hdlist1">
Access message content
</dt>
<dd>
<p>
<a href="zmq_msg_data.html">zmq_msg_data(3)</a>
<a href="zmq_msg_size.html">zmq_msg_size(3)</a>
<a href="zmq_msg_more.html">zmq_msg_more(3)</a>
</p>
</dd>
<dt class="hdlist1">
Work with message properties
</dt>
<dd>
<p>
<a href="zmq_msg_gets.html">zmq_msg_gets(3)</a>
<a href="zmq_msg_get.html">zmq_msg_get(3)</a>
<a href="zmq_msg_set.html">zmq_msg_set(3)</a>
</p>
</dd>
<dt class="hdlist1">
Message manipulation
</dt>
<dd>
<p>
<a href="zmq_msg_copy.html">zmq_msg_copy(3)</a>
<a href="zmq_msg_move.html">zmq_msg_move(3)</a>
</p>
</dd>
</dl></div>
</div>
<div class="sect2">
<h3 id="_sockets">Sockets</h3>
<div class="paragraph"><p>ØMQ sockets present an abstraction of an asynchronous <em>message queue</em>, with the
exact queueing semantics depending on the socket type in use. See
<a href="zmq_socket.html">zmq_socket(3)</a> for the socket types provided.</p></div>
<div class="paragraph"><p>The following functions are provided to work with sockets:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
Creating a socket
</dt>
<dd>
<p>
<a href="zmq_socket.html">zmq_socket(3)</a>
</p>
</dd>
<dt class="hdlist1">
Closing a socket
</dt>
<dd>
<p>
<a href="zmq_close.html">zmq_close(3)</a>
</p>
</dd>
<dt class="hdlist1">
Manipulating socket options
</dt>
<dd>
<p>
<a href="zmq_getsockopt.html">zmq_getsockopt(3)</a>
<a href="zmq_setsockopt.html">zmq_setsockopt(3)</a>
</p>
</dd>
<dt class="hdlist1">
Establishing a message flow
</dt>
<dd>
<p>
<a href="zmq_bind.html">zmq_bind(3)</a>
<a href="zmq_connect.html">zmq_connect(3)</a>
</p>
</dd>
<dt class="hdlist1">
Sending and receiving messages
</dt>
<dd>
<p>
<a href="zmq_msg_send.html">zmq_msg_send(3)</a>
<a href="zmq_msg_recv.html">zmq_msg_recv(3)</a>
<a href="zmq_send.html">zmq_send(3)</a>
<a href="zmq_recv.html">zmq_recv(3)</a>
<a href="zmq_send_const.html">zmq_send_const(3)</a>
</p>
</dd>
<dt class="hdlist1">
Monitoring socket events
</dt>
<dd>
<p>
<a href="zmq_socket_monitor.html">zmq_socket_monitor(3)</a>
</p>
</dd>
</dl></div>
<div class="paragraph"><div class="title">Input/output multiplexing</div><p>ØMQ provides a mechanism for applications to multiplex input/output events over
a set containing both ØMQ sockets and standard sockets. This mechanism mirrors
the standard <em>poll()</em> system call, and is described in detail in
<a href="zmq_poll.html">zmq_poll(3)</a>. This API is deprecated, however.</p></div>
<div class="paragraph"><p>There is a new DRAFT API with multiple zmq_poller_* function, which is described
in <a href="zmq_poller.html">zmq_poller(3)</a>.</p></div>
</div>
<div class="sect2">
<h3 id="_transports">Transports</h3>
<div class="paragraph"><p>A ØMQ socket can use multiple different underlying transport mechanisms.
Each transport mechanism is suited to a particular purpose and has its own
advantages and drawbacks.</p></div>
<div class="paragraph"><p>The following transport mechanisms are provided:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
Unicast transport using TCP
</dt>
<dd>
<p>
<a href="zmq_tcp.html">zmq_tcp(7)</a>
</p>
</dd>
<dt class="hdlist1">
Reliable multicast transport using PGM
</dt>
<dd>
<p>
<a href="zmq_pgm.html">zmq_pgm(7)</a>
</p>
</dd>
<dt class="hdlist1">
Local inter-process communication transport
</dt>
<dd>
<p>
<a href="zmq_ipc.html">zmq_ipc(7)</a>
</p>
</dd>
<dt class="hdlist1">
Local in-process (inter-thread) communication transport
</dt>
<dd>
<p>
<a href="zmq_inproc.html">zmq_inproc(7)</a>
</p>
</dd>
<dt class="hdlist1">
Virtual Machine Communications Interface (VMC) transport
</dt>
<dd>
<p>
<a href="zmq_vmci.html">zmq_vmci(7)</a>
</p>
</dd>
<dt class="hdlist1">
Unreliable unicast and multicast using UDP
</dt>
<dd>
<p>
<a href="zmq_udp.html">zmq_udp(7)</a>
</p>
</dd>
</dl></div>
</div>
<div class="sect2">
<h3 id="_proxies">Proxies</h3>
<div class="paragraph"><p>ØMQ provides <em>proxies</em> to create fanout and fan-in topologies. A proxy connects
a <em>frontend</em> socket to a <em>backend</em> socket and switches all messages between the
two sockets, opaquely. A proxy may optionally capture all traffic to a third
socket. To start a proxy in an application thread, use <a href="zmq_proxy.html">zmq_proxy(3)</a>.</p></div>
</div>
<div class="sect2">
<h3 id="_security">Security</h3>
<div class="paragraph"><p>A ØMQ socket can select a security mechanism. Both peers must use the same
security mechanism.</p></div>
<div class="paragraph"><p>The following security mechanisms are provided for IPC and TCP connections:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
Null security
</dt>
<dd>
<p>
<a href="zmq_null.html">zmq_null(7)</a>
</p>
</dd>
<dt class="hdlist1">
Plain-text authentication using username and password
</dt>
<dd>
<p>
<a href="zmq_plain.html">zmq_plain(7)</a>
</p>
</dd>
<dt class="hdlist1">
Elliptic curve authentication and encryption
</dt>
<dd>
<p>
<a href="zmq_curve.html">zmq_curve(7)</a>
</p>
</dd>
<dt class="hdlist1">
Generate a CURVE keypair in armored text format
</dt>
<dd>
<p>
<a href="zmq_curve_keypair.html">zmq_curve_keypair(3)</a>
</p>
</dd>
</dl></div>
<div class="paragraph"><p>Derive a CURVE public key from a secret key:
<a href="zmq_curve_public.html">zmq_curve_public(3)</a></p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
Converting keys to/from armoured text strings
</dt>
<dd>
<p>
<a href="zmq_z85_decode.html">zmq_z85_decode(3)</a>
<a href="zmq_z85_encode.html">zmq_z85_encode(3)</a>
</p>
</dd>
</dl></div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_error_handling">ERROR HANDLING</h2>
<div class="sectionbody">
<div class="paragraph"><p>The ØMQ library functions handle errors using the standard conventions found on
POSIX systems. Generally, this means that upon failure a ØMQ library function
shall return either a NULL value (if returning a pointer) or a negative value
(if returning an integer), and the actual error code shall be stored in the
<em>errno</em> variable.</p></div>
<div class="paragraph"><p>On non-POSIX systems some users may experience issues with retrieving the
correct value of the <em>errno</em> variable. The <em>zmq_errno()</em> function is provided
to assist in these cases; for details refer to <a href="zmq_errno.html">zmq_errno(3)</a>.</p></div>
<div class="paragraph"><p>The <em>zmq_strerror()</em> function is provided to translate ØMQ-specific error codes
into error message strings; for details refer to <a href="zmq_strerror.html">zmq_strerror(3)</a>.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_utility">UTILITY</h2>
<div class="sectionbody">
<div class="paragraph"><p>The following utility functions are provided:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
Working with atomic counters
</dt>
<dd>
<p>
<a href="zmq_atomic_counter_new.html">zmq_atomic_counter_new(3)</a>
<a href="zmq_atomic_counter_set.html">zmq_atomic_counter_set(3)</a>
<a href="zmq_atomic_counter_inc.html">zmq_atomic_counter_inc(3)</a>
<a href="zmq_atomic_counter_dec.html">zmq_atomic_counter_dec(3)</a>
<a href="zmq_atomic_counter_value.html">zmq_atomic_counter_value(3)</a>
<a href="zmq_atomic_counter_destroy.html">zmq_atomic_counter_destroy(3)</a>
</p>
</dd>
</dl></div>
</div>
</div>
<div class="sect1">
<h2 id="_miscellaneous">MISCELLANEOUS</h2>
<div class="sectionbody">
<div class="paragraph"><p>The following miscellaneous functions are provided:</p></div>
<div class="dlist"><dl>
<dt class="hdlist1">
Report ØMQ library version
</dt>
<dd>
<p>
<a href="zmq_version.html">zmq_version(3)</a>
</p>
</dd>
</dl></div>
</div>
</div>
<div class="sect1">
<h2 id="_language_bindings">LANGUAGE BINDINGS</h2>
<div class="sectionbody">
<div class="paragraph"><p>The ØMQ library provides interfaces suitable for calling from programs in any
language; this documentation documents those interfaces as they would be used
by C programmers. The intent is that programmers using ØMQ from other languages
shall refer to this documentation alongside any documentation provided by the
vendor of their language binding.</p></div>
<div class="paragraph"><p>Language bindings (C++, Python, PHP, Ruby, Java and more) are provided by
members of the ØMQ community and pointers can be found on the ØMQ website.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_authors">AUTHORS</h2>
<div class="sectionbody">
<div class="paragraph"><p>This page was written by the ØMQ community. To make a change please
read the ØMQ Contribution Policy at <a href="http://www.zeromq.org/docs:contributing">http://www.zeromq.org/docs:contributing</a>.</p></div>
</div>
</div>
<div class="sect1">
<h2 id="_resources">RESOURCES</h2>
<div class="sectionbody">
<div class="paragraph"><p>Main web site: <a href="http://www.zeromq.org/">http://www.zeromq.org/</a></p></div>
<div class="paragraph"><p>Report bugs to the ØMQ development mailing list: <<a href="mailto:zeromq-dev@lists.zeromq.org">zeromq-dev@lists.zeromq.org</a>></p></div>
</div>
</div>
<div class="sect1">
<h2 id="_copying">COPYING</h2>
<div class="sectionbody">
<div class="paragraph"><p>Free use of this software is granted under the terms of the GNU Lesser General
Public License (LGPL). For details see the files <code>COPYING</code> and <code>COPYING.LESSER</code>
included with the ØMQ distribution.</p></div>
</div>
</div>
</div>
<div id="footnotes"><hr /></div>
<div id="footer">
<div id="footer-text">
ØMQ 4.3.2<br />
Last updated 2019-07-08 16:19:27 UTC
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