zmq - 0MQ lightweight messaging kernel
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
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
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
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
Sending and receiving messages
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
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
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
The 0MQ documentation was written by Martin Sustrik
<firstname.lastname@example.org> and Martin Lucina <email@example.com>.
Main web site: http://www.zeromq.org/
Report bugs to the 0MQ development mailing list:
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.