1ZMQ(7)                            0MQ Manual                            ZMQ(7)
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NAME

6       zmq - 0MQ lightweight messaging kernel
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SYNOPSIS

9       #include <zmq.h>
10
11       cc [flags] files -lzmq [libraries]
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DESCRIPTION

14       The 0MQ lightweight messaging kernel is a library which extends the
15       standard socket interfaces with features traditionally provided by
16       specialised messaging middleware products. 0MQ sockets provide an
17       abstraction of asynchronous message queues, multiple messaging
18       patterns, message filtering (subscriptions), seamless access to
19       multiple transport protocols and more.
20
21       This documentation presents an overview of 0MQ concepts, describes how
22       0MQ abstracts standard sockets and provides a reference manual for the
23       functions provided by the 0MQ library.
24
25   Context
26       The 0MQ context keeps the list of sockets and manages the async I/O
27       thread and internal queries.
28
29       Before using any 0MQ library functions you must create a 0MQ context.
30       When you exit your application you must destroy the context. These
31       functions let you work with contexts:
32
33       Create a new 0MQ context
34           zmq_ctx_new(3)
35
36       Work with context properties
37           zmq_ctx_set(3) zmq_ctx_get(3)
38
39       Destroy a 0MQ context
40           zmq_ctx_shutdown(3) zmq_ctx_term(3)
41
42       Thread safety
43           A 0MQ context is thread safe and may be shared among as many
44           application threads as necessary, without any additional locking
45           required on the part of the caller.
46
47           Individual 0MQ sockets are not thread safe except in the case where
48           full memory barriers are issued when migrating a socket from one
49           thread to another. In practice this means applications can create a
50           socket in one thread with zmq_socket() and then pass it to a newly
51           created thread as part of thread initialisation, for example via a
52           structure passed as an argument to pthread_create().
53
54       Multiple contexts
55           Multiple contexts may coexist within a single application. Thus, an
56           application can use 0MQ directly and at the same time make use of
57           any number of additional libraries or components which themselves
58           make use of 0MQ as long as the above guidelines regarding thread
59           safety are adhered to.
60
61   Messages
62       A 0MQ message is a discrete unit of data passed between applications or
63       components of the same application. 0MQ messages have no internal
64       structure and from the point of view of 0MQ itself they are considered
65       to be opaque binary data.
66
67       The following functions are provided to work with messages:
68
69       Initialise a message
70           zmq_msg_init(3) zmq_msg_init_size(3) zmq_msg_init_buffer(3)
71           zmq_msg_init_data(3)
72
73       Sending and receiving a message
74           zmq_msg_send(3) zmq_msg_recv(3)
75
76       Release a message
77           zmq_msg_close(3)
78
79       Access message content
80           zmq_msg_data(3) zmq_msg_size(3) zmq_msg_more(3)
81
82       Work with message properties
83           zmq_msg_gets(3) zmq_msg_get(3) zmq_msg_set(3)
84
85       Message manipulation
86           zmq_msg_copy(3) zmq_msg_move(3)
87
88   Sockets
89       0MQ sockets present an abstraction of an asynchronous message queue,
90       with the exact queueing semantics depending on the socket type in use.
91       See zmq_socket(3) for the socket types provided.
92
93       The following functions are provided to work with sockets:
94
95       Creating a socket
96           zmq_socket(3)
97
98       Closing a socket
99           zmq_close(3)
100
101       Manipulating socket options
102           zmq_getsockopt(3) zmq_setsockopt(3)
103
104       Establishing a message flow
105           zmq_bind(3) zmq_connect(3)
106
107       Sending and receiving messages
108           zmq_msg_send(3) zmq_msg_recv(3) zmq_send(3) zmq_recv(3)
109           zmq_send_const(3)
110
111       Monitoring socket events
112           zmq_socket_monitor(3)
113
114       Input/output multiplexing. 0MQ provides a mechanism for applications to
115       multiplex input/output events over a set containing both 0MQ sockets
116       and standard sockets. This mechanism mirrors the standard poll() system
117       call, and is described in detail in zmq_poll(3). This API is
118       deprecated, however.
119
120       There is a new DRAFT API with multiple zmq_poller_* function, which is
121       described in zmq_poller(3).
122
123   Transports
124       A 0MQ socket can use multiple different underlying transport
125       mechanisms. Each transport mechanism is suited to a particular purpose
126       and has its own advantages and drawbacks.
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128       The following transport mechanisms are provided:
129
130       Unicast transport using TCP
131           zmq_tcp(7)
132
133       Reliable multicast transport using PGM
134           zmq_pgm(7)
135
136       Local inter-process communication transport
137           zmq_ipc(7)
138
139       Local in-process (inter-thread) communication transport
140           zmq_inproc(7)
141
142       Virtual Machine Communications Interface (VMC) transport
143           zmq_vmci(7)
144
145       Unreliable unicast and multicast using UDP
146           zmq_udp(7)
147
148   Proxies
149       0MQ provides proxies to create fanout and fan-in topologies. A proxy
150       connects a frontend socket to a backend socket and switches all
151       messages between the two sockets, opaquely. A proxy may optionally
152       capture all traffic to a third socket. To start a proxy in an
153       application thread, use zmq_proxy(3).
154
155   Security
156       A 0MQ socket can select a security mechanism. Both peers must use the
157       same security mechanism.
158
159       The following security mechanisms are provided for IPC and TCP
160       connections:
161
162       Null security
163           zmq_null(7)
164
165       Plain-text authentication using username and password
166           zmq_plain(7)
167
168       Elliptic curve authentication and encryption
169           zmq_curve(7)
170
171       Generate a CURVE keypair in armored text format
172           zmq_curve_keypair(3)
173
174       Derive a CURVE public key from a secret key: zmq_curve_public(3)
175
176       Converting keys to/from armoured text strings
177           zmq_z85_decode(3) zmq_z85_encode(3)
178

ERROR HANDLING

180       The 0MQ library functions handle errors using the standard conventions
181       found on POSIX systems. Generally, this means that upon failure a 0MQ
182       library function shall return either a NULL value (if returning a
183       pointer) or a negative value (if returning an integer), and the actual
184       error code shall be stored in the errno variable.
185
186       On non-POSIX systems some users may experience issues with retrieving
187       the correct value of the errno variable. The zmq_errno() function is
188       provided to assist in these cases; for details refer to zmq_errno(3).
189
190       The zmq_strerror() function is provided to translate 0MQ-specific error
191       codes into error message strings; for details refer to zmq_strerror(3).
192

UTILITY

194       The following utility functions are provided:
195
196       Working with atomic counters
197           zmq_atomic_counter_new(3) zmq_atomic_counter_set(3)
198           zmq_atomic_counter_inc(3) zmq_atomic_counter_dec(3)
199           zmq_atomic_counter_value(3) zmq_atomic_counter_destroy(3)
200

MISCELLANEOUS

202       The following miscellaneous functions are provided:
203
204       Report 0MQ library version
205           zmq_version(3)
206

LANGUAGE BINDINGS

208       The 0MQ library provides interfaces suitable for calling from programs
209       in any language; this documentation documents those interfaces as they
210       would be used by C programmers. The intent is that programmers using
211       0MQ from other languages shall refer to this documentation alongside
212       any documentation provided by the vendor of their language binding.
213
214       Language bindings (C++, Python, PHP, Ruby, Java and more) are provided
215       by members of the 0MQ community and pointers can be found on the 0MQ
216       website.
217

AUTHORS

219       This page was written by the 0MQ community. To make a change please
220       read the 0MQ Contribution Policy at
221       http://www.zeromq.org/docs:contributing.
222

RESOURCES

224       Main web site: http://www.zeromq.org/
225
226       Report bugs to the 0MQ development mailing list:
227       <zeromq-dev@lists.zeromq.org[1]>
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COPYING

230       Free use of this software is granted under the terms of the GNU Lesser
231       General Public License (LGPL). For details see the files COPYING and
232       COPYING.LESSER included with the 0MQ distribution.
233

NOTES

235        1. zeromq-dev@lists.zeromq.org
236           mailto:zeromq-dev@lists.zeromq.org
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2400MQ 4.3.4                         07/23/2021                            ZMQ(7)
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