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
       The 0MQ context keeps the list of sockets and manages the async I/O thread and internal
       queries.

       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
           zmq_ctx_new(3)

       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 initialisation, 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_buffer(3) zmq_msg_init_data(3)

       Sending and receiving a message
           zmq_msg_send(3) zmq_msg_recv(3)

       Release a message
           zmq_msg_close(3)

       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)

   Sockets
       0MQ sockets present an abstraction of an 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_msg_send(3) zmq_msg_recv(3) zmq_send(3) zmq_recv(3) zmq_send_const(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). This API is deprecated, however.

       There is a new DRAFT API with multiple zmq_poller_* function, which is described in
       zmq_poller(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)

       Virtual Machine Communications Interface (VMC) transport
           zmq_vmci(7)

       Unreliable unicast and multicast using UDP
           zmq_udp(7)

   Proxies
       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).

   Security
       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 connections:

       Null security
           zmq_null(7)

       Plain-text authentication using username and password
           zmq_plain(7)

       Elliptic curve authentication and encryption
           zmq_curve(7)

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

       Derive a CURVE public key from a secret key: zmq_curve_public(3)

       Converting keys to/from armoured text strings
           zmq_z85_decode(3) zmq_z85_encode(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).

UTILITY

       The following utility functions are provided:

       Working with atomic counters
           zmq_atomic_counter_new(3) zmq_atomic_counter_set(3) zmq_atomic_counter_inc(3)
           zmq_atomic_counter_dec(3) zmq_atomic_counter_value(3) zmq_atomic_counter_destroy(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.

       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 website.

AUTHORS

       This page was written by the 0MQ community. To make a change please read the 0MQ
       Contribution Policy at http://www.zeromq.org/docs:contributing.

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