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ZMQ(7)				  0MQ Manual				ZMQ(7)

       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 you must create a	0MQ context.
       When you	exit your application you must destroy the context. These
       functions let you work with contexts:

       Create a	new 0MQ	context


       Work with context properties

	   zmq_ctx_set(3) zmq_ctx_get(3)

       Destroy a 0MQ context

	   zmq_ctx_shutdown(3) zmq_ctx_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.

       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)

       Sending and receiving a message

	   zmq_msg_send(3) zmq_msg_recv(3)

       Release a message


       Access message content

	   zmq_msg_data(3) zmq_msg_size(3) zmq_msg_more(3)

       Work with message properties

	   zmq_msg_gets(3) zmq_msg_get(3) zmq_msg_set(3)

       Message manipulation

	   zmq_msg_copy(3) zmq_msg_move(3)

       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


       Closing a socket


       Manipulating socket options

	   zmq_getsockopt(3) zmq_setsockopt(3)

       Establishing a message flow

	   zmq_bind(3) zmq_connect(3)

       Sending and receiving messages

	   zmq_msg_send(3) zmq_msg_recv(3) zmq_send(3) zmq_recv(3)

       Monitoring socket events: zmq_socket_monitor(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


       0MQ provides proxies to create fanout and fan-in	topologies. A proxy
       connects	a frontend socket to a backend 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 zmq_proxy(3).

       A 0MQ socket can	select a security mechanism. Both peers	must use the
       same security mechanism.

       The following security mechanisms are provided for IPC and TCP

       Null security


       Plain-text authentication using username	and password


       Elliptic	curve authentication and encryption


       Generate	a CURVE	keypair	in armored text	format:	zmq_curve_keypair(3)

       Convert an armored key into a 32-byte binary key: zmq_z85_decode(3)

       Convert a 32-byte binary	CURVE key to an	armored	text string:

       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).

       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.

       Language	bindings (C++, Python, PHP, Ruby, Java and more) are provided
       by members of the 0MQ community and pointers can	be found on the	0MQ

       This page was written by	the 0MQ	community. To make a change please
       read the	0MQ Contribution Policy	at

       Main web	site:

       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.


0MQ 4.1.5			  07/02/2017				ZMQ(7)


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