Langue: en

Autres versions - même langue

Version: 03/16/2010 (ubuntu - 25/10/10)

Section: 7 (Divers)


zmq - 0MQ lightweight messaging kernel


#include <zmq.h>

cc [flags] files -lzmq [libraries]


The 0MQ lightweight messaging kernel is a library which extends the standard socket interfaces with features traditionally provided by specialised messaging middleware products. 0MQ sockets provide an abstraction of asynchronous message queues, multiple messaging patterns, message filtering (subscriptions), seamless access to multiple transport protocols and more.

This documentation presents an overview of 0MQ concepts, describes how 0MQ abstracts standard sockets and provides a reference manual for the functions provided by the 0MQ library.


Before using any 0MQ library functions the caller must initialise a 0MQ context using zmq_init(). The following functions are provided to handle initialisation and termination of a context:

Initialise 0MQ context


Terminate 0MQ context


Thread safety

A 0MQ context is thread safe and may be shared among as many application threads as the application has requested using the app_threads parameter to zmq_init(), without any additional locking required on the part of the caller. Each 0MQ socket belonging to a particular context may only be used by the thread that created it using zmq_socket().

Multiple contexts

Multiple contexts may coexist within a single application. Thus, an application can use 0MQ directly and at the same time make use of any number of additional libraries or components which themselves make use of 0MQ as long as the above guidelines regarding thread safety are adhered to.


A 0MQ message is a discrete unit of data passed between applications or components of the same application. 0MQ messages have no internal structure and from the point of view of 0MQ itself they are considered to be opaque binary data.

The following functions are provided to work with messages:

Initialise a message

zmq_msg_init(3) zmq_msg_init_size(3) zmq_msg_init_data(3)

Release a message


Access message content

zmq_msg_data(3) zmq_msg_size(3)

Message manipulation

zmq_msg_copy(3) zmq_msg_move(3)


Standard sockets present a synchronous interface to either connection-mode reliable byte streams (SOCK_STREAM), or connection-less unreliable datagrams (SOCK_DGRAM). In comparison, 0MQ sockets present an abstraction of a asynchronous message queue, with the exact queueing semantics depending on the socket type (messaging pattern) in use. See zmq_socket(3) for the messaging patterns provided.

0MQ sockets being asynchronous means that the timings of the physical connection setup and teardown, reconnect and effective delivery are organized by 0MQ itself, and that messages may be queued in the event that a peer is unavailable to receive them.

The following functions are provided to work with sockets:

Creating a socket


Closing a socket


Setting socket options


Establishing a message flow

zmq_bind(3) zmq_connect(3)

Sending and receiving messages

zmq_send(3) zmq_recv(3)

Input/output multiplexing

0MQ provides a mechanism for applications to multiplex input/output events over a set containing both 0MQ sockets and standard sockets. This mechanism mirrors the standard poll() system call, and is described in detail in zmq_poll(3).


A 0MQ socket can use multiple different underlying transport mechanisms. Each transport mechanism is suited to a particular purpose and has its own advantages and drawbacks.

The following transport mechanisms are provided:

Unicast transport using TCP


Reliable multicast transport using PGM


Local inter-process communication transport


Local in-process (inter-thread) communication transport



Apart from the 0MQ library the 0MQ distribution includes devices which are building blocks intended to serve as intermediate nodes in complex messaging topologies.

The following devices are provided:

Forwarder device for request-response messaging


Forwarder device for publish-subscribe messaging


Streamer device for parallelized pipeline messaging



The 0MQ library functions handle errors using the standard conventions found on POSIX systems. Generally, this means that upon failure a 0MQ 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 errno variable.

A zmq_strerror() function is provided to translate 0MQ-specific error codes into error message strings. For further details refer to zmq_strerror(3).


The following miscellaneous functions are provided:

Report 0MQ library version



The 0MQ 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 0MQ from other languages shall refer to this documentation alongside any documentation provided by the vendor of their language binding.

C++ language binding

The 0MQ distribution includes a C++ language binding, which is documented separately in zmq_cpp(7).

Other language bindings

Other language bindings (Python, Ruby, Java and more) are provided by members of the 0MQ community and pointers can be found on the 0MQ website.


The 0MQ documentation was written by Martin Sustrik <m[blue]sustrik@250bpm.comm[][1]> and Martin Lucina <m[blue]mato@kotelna.skm[][2]>.


Main web site: m[blue][]

Report bugs to the 0MQ development mailing list: <m[blue]zeromq-dev@lists.zeromq.orgm[][3]>


Free use of this software is granted under the terms of the GNU Lesser General Public License (LGPL). For details see the files COPYING and COPYING.LESSER included with the 0MQ distribution.