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@@ -9,59 +9,69 @@ zmq - 0MQ lightweight messaging kernel | |
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SYNOPSIS | ||
-------- | ||
0MQ is an extension of POSIX sockets. It is a library that augments standard | ||
networking sockets by special capabilities that you can otherwise get only | ||
by using specialised "messaging middleware" products, such as automated | ||
handling of connections and disconnections, delivery of a message to multiple | ||
destinations, load balancing messages, sophisticated message filtering etc. | ||
*#include <zmq.h>* | ||
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0MQ is designed to be extremely fast. Expected end-to-end latencies for | ||
messages passed over a LAN are in tens of microseconds. Expected | ||
throughputs are to be measured in millions of messages per second. | ||
*cc* ['flags'] 'files' *-lzmq* ['libraries'] | ||
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0MQ is designed to be very thin. It requires no more than couple of | ||
pages in resident memory and is thus well suited for any environment ranging | ||
from small embedded devices, routers and cell phones to enterprise-scale | ||
data centers. | ||
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0MQ runs on a wide range of operating systems and supports variety of processor | ||
microarchitectures. | ||
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. | ||
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0MQ is accessible from a large set of programming languages. | ||
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. | ||
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0MQ is fully open sourced LGPL-licensed software. | ||
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CONTEXT | ||
------- | ||
Each 0MQ socket lives within a specific context. Creating and destroying | ||
context is a counterpart of library initialisation/deinitialisation as used | ||
elsewhere. Ability to create multiple contexts saves the day when an application | ||
happens to link (indirectly and involuntarily) with several instances of 0MQ. | ||
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': | ||
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Initialise 0MQ context:: | ||
linkzmq:zmq_init[3] | ||
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Uninitialise 0MQ context:: | ||
Terminate 0MQ context:: | ||
linkzmq:zmq_term[3] | ||
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MESSAGES | ||
-------- | ||
Message is a discrete unit of data passed between applications or components | ||
of the same application. 0MQ message has no internal structure, it is an opaque | ||
BLOB. When writing data to or reading data from the message, you are free to | ||
use any of the many serialisation libraries available. Alternatively, you can | ||
use your own serialisation code. The latter option is especially useful when | ||
migrating legacy applications to 0MQ - there's no need to break existing | ||
message formats. | ||
Thread safety | ||
^^^^^^^^^^^^^ | ||
A 0MQ 'context' is thread safe and may be shared among as many application | ||
threads as the application has requested using the _app_threads_ parameter to | ||
_zmq_init()_, without any additional locking required on the part of the | ||
caller. Each 0MQ socket belonging to a particular 'context' may only be used | ||
by *the thread that created it* using _zmq_socket()_. | ||
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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. | ||
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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 BLOBs. | ||
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The following functions are provided to work with messages: | ||
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Initialise a message:: | ||
linkzmq:zmq_msg_init[3] | ||
linkzmq:zmq_msg_size[3] | ||
linkzmq:zmq_msg_data[3] | ||
linkzmq:zmq_msg_init_size[3] | ||
linkzmq:zmq_msg_init_data[3] | ||
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Uninitialise a message:: | ||
Release a message:: | ||
linkzmq:zmq_msg_close[3] | ||
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Access message content:: | ||
|
@@ -73,10 +83,21 @@ Message manipulation:: | |
linkzmq:zmq_msg_move[3] | ||
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SOCKETS | ||
------- | ||
0MQ sockets are very similar to POSIX sockets. See following manual pages to | ||
understand them in depth. | ||
Sockets | ||
~~~~~~~ | ||
Standard sockets present a _synchronous_ interface to either connection-mode | ||
reliable byte streams (SOCK_STREAM), or connection-less unreliable datagrams | ||
(SOCK_DGRAM). In comparison, 0MQ sockets present an abstraction of a | ||
asynchronous _message queue_, with the exact queueing semantics depending on | ||
the socket type (_messaging pattern_) in use. See linkzmq:zmq_socket[3] for the | ||
_messaging patterns_ provided. | ||
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0MQ sockets being _asynchronous_ means that the timings of the physical | ||
connection setup and teardown, reconnect and effective delivery are organized | ||
by 0MQ itself, and that messages may be _queued_ in the event that a peer is | ||
unavailable to receive them. | ||
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The following functions are provided to work with sockets: | ||
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Creating a socket:: | ||
linkzmq:zmq_socket[3] | ||
|
@@ -91,82 +112,108 @@ Establishing a message flow:: | |
linkzmq:zmq_bind[3] | ||
linkzmq:zmq_connect[3] | ||
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Sending & receiving messages:: | ||
Sending and receiving messages:: | ||
linkzmq:zmq_send[3] | ||
linkzmq:zmq_flush[3] | ||
linkzmq:zmq_recv[3] | ||
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MULTIPLEXING | ||
------------ | ||
0MQ allows you to handle multiple sockets (0MQ as well as standard POSIX) | ||
in an asynchronous manner. | ||
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Poll for I/O events:: | ||
linkzmq:zmq_poll[3] | ||
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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 | ||
linkzmq:zmq_poll[3]. | ||
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ERROR HANDLING | ||
-------------- | ||
0MQ defines couple of non-POSIX error codes. Use following functions to handle | ||
them neatly. | ||
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Convert error code into human readable string:: | ||
linkzmq:zmq_strerror[3] | ||
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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. | ||
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TRANSPORTS | ||
---------- | ||
0MQ allows for using different underlying transport mechanisms (even multiple | ||
at once). Each transport mechanism has its own advantages and drawbacks. For | ||
detailed description of individual mechanisms check following manual pages: | ||
The following transport mechanisms are provided: | ||
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TCP/IP transport:: | ||
Unicast transport using TCP:: | ||
linkzmq:zmq_tcp[7] | ||
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UDP reliable multicast transport:: | ||
linkzmq:zmq_udp[7] | ||
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PGM reliable multicast transport:: | ||
Reliable multicast transport using PGM:: | ||
linkzmq:zmq_pgm[7] | ||
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Inter-process transport:: | ||
Local inter-process communication transport:: | ||
linkzmq:zmq_ipc[7] | ||
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In-process (inter-thread) transport:: | ||
Local in-process (inter-thread) communication transport:: | ||
linkzmq:zmq_inproc[7] | ||
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DEVICES | ||
------- | ||
Aside of the messaging library (a.k.a. messaging kernel) 0MQ provides pre-built | ||
executables - devices - to serve as middle nodes in complex messaging | ||
topologies. For detailed description of individual devices check following | ||
manual pages: | ||
Devices | ||
~~~~~~~ | ||
Apart from the 0MQ library the 0MQ distribution includes 'devices' which are | ||
building blocks intended to serve as intermediate nodes in complex messaging | ||
topologies. | ||
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Forwarder device for PUB/SUB messaging:: | ||
The following devices are provided: | ||
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Forwarder device for request-response messaging:: | ||
linkzmq:zmq_queue[1] | ||
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Forwarder device for publish-subscribe messaging:: | ||
linkzmq:zmq_forwarder[1] | ||
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Streamer device for UPSTREAM/DOWNSTREAM messaging:: | ||
Streamer device for parallelized pipeline messaging:: | ||
linkzmq:zmq_streamer[1] | ||
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Forwarder device for REQ/REP messaging:: | ||
linkzmq:zmq_queue[1] | ||
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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. | ||
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A _zmq_strerror()_ function is provided to translate 0MQ-specific error codes | ||
into error message strings. For further details refer to | ||
linkzmq:zmq_strerror[3]. | ||
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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. | ||
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LANGUAGES | ||
--------- | ||
0MQ manual pages provide info on C API. To find out how the your | ||
favourite language API maps to C API and thus how to find relevant manual pages, | ||
see following articles: | ||
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$$C++$$:: | ||
linkzmq:zmq_cpp[7] | ||
C++ language binding | ||
~~~~~~~~~~~~~~~~~~~~ | ||
The 0MQ distribution includes a $$C++$$ language binding, which is documented | ||
separately in linkzmq:zmq_cpp[7]. | ||
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Java:: | ||
linkzmq:zmq_java[7] | ||
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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. | ||
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AUTHOR | ||
------ | ||
Martin Sustrik <sustrik at 250bpm dot com> | ||
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AUTHORS | ||
------- | ||
The 0MQ documentation was written by Martin Sustrik <[email protected]> and | ||
Martin Lucina <[email protected]>. | ||
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RESOURCES | ||
--------- | ||
Main web site: <http://www.zeromq.org/> | ||
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Report bugs to the 0MQ development mailing list: <[email protected]> | ||
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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. |
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