Provided by: libzmq-dev_2.2.0+dfsg-7_amd64 
NAME
zmq - 0MQ lightweight messaging kernel
SYNOPSIS
#include <zmq.h>
cc [flags] files -lzmq [libraries]
DESCRIPTION
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.
Context
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
zmq_init(3)
Terminate 0MQ context
zmq_term(3)
Thread safety
A 0MQ context 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.
Individual 0MQ sockets are not 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 zmq_socket() and then pass it to a newly created thread as part of thread
initialization, for example via a structure passed as an argument to pthread_create().
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.
Messages
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
zmq_msg_close(3)
Access message content
zmq_msg_data(3) zmq_msg_size(3)
Message manipulation
zmq_msg_copy(3) zmq_msg_move(3)
Sockets
0MQ sockets present an abstraction of a asynchronous message queue, with the exact queueing semantics
depending on the socket type in use. See zmq_socket(3) for the socket types provided.
The following functions are provided to work with sockets:
Creating a socket
zmq_socket(3)
Closing a socket
zmq_close(3)
Manipulating socket options
zmq_getsockopt(3) zmq_setsockopt(3)
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).
Transports
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
zmq_tcp(7)
Reliable multicast transport using PGM
zmq_pgm(7)
Local inter-process communication transport
zmq_ipc(7)
Local in-process (inter-thread) communication transport
zmq_inproc(7)
Devices
0MQ provides devices, which are building blocks that act as intermediate nodes in complex messaging
topologies. Devices can act as brokers that other nodes connect to, proxies that connect through to other
nodes, or any mix of these two models.
You can start a device in an application thread, see zmq_device(3).
ERROR HANDLING
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.
On non-POSIX systems some users may experience issues with retrieving the correct value of the errno
variable. The zmq_errno() function is provided to assist in these cases; for details refer to
zmq_errno(3).
The zmq_strerror() function is provided to translate 0MQ-specific error codes into error message strings;
for details refer to zmq_strerror(3).
MISCELLANEOUS
The following miscellaneous functions are provided:
Report 0MQ library version
zmq_version(3)
LANGUAGE BINDINGS
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.
AUTHORS
This manual page was written by the 0MQ community.
RESOURCES
Main web site: http://www.zeromq.org/ Report bugs to the 0MQ development mailing list: <zeromq-dev@lists.zeromq.org[1]>
COPYING
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.
NOTES
1. zeromq-dev@lists.zeromq.org mailto:zeromq-dev@lists.zeromq.org