ZMQ(7) 0MQ Manual ZMQ(7)NAMEzmq - 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
0MQ 2.2.0 04/04/2012 ZMQ(7)
