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<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision: 1.3 $ -->
<!-- Purpose: fileprocess.process -->
<!-- Membership: bundled -->
<book xml:id="book.sem" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
<title>Semaphore, Shared Memory and IPC </title>
<titleabbrev>Semaphore</titleabbrev>
<!-- {{{ preface -->
<preface xml:id="intro.sem">
&reftitle.intro;
<para>
This module provides wrappers for the System V IPC family of functions.
It includes semaphores, shared memory and inter-process messaging (IPC).
</para>
<para>
Semaphores may be used to provide exclusive access to
resources on the current machine, or to limit the number of
processes that may simultaneously use a resource.
</para>
<para>
This module provides also shared memory functions using System V
shared memory. Shared memory may be used to provide access to
global variables. Different httpd-daemons and even other programs
(such as Perl, C, ...) are able to access this data to provide a
global data-exchange. Remember, that shared memory is NOT safe
against simultaneous access. Use semaphores for synchronization.
<table>
<title>Limits of Shared Memory by the Unix OS</title>
<tgroup cols="2">
<tbody>
<row>
<entry>SHMMAX</entry>
<entry>max size of shared memory, normally 131072 bytes</entry>
</row>
<row>
<entry>SHMMIN</entry>
<entry>minimum size of shared memory, normally 1 byte</entry>
</row>
<row>
<entry>SHMMNI</entry>
<entry>
max amount of shared memory segments on a system,
normally 100
</entry>
</row>
<row>
<entry>SHMSEG</entry>
<entry>
max amount of shared memory segments per process, normally 6
</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
<para>
The messaging functions may be used to send and receive messages to/from
other processes. They provide a simple and effective means of exchanging
data between processes, without the need for setting up an alternative
using Unix domain sockets.
</para>
¬e.no-windows.extension;
</preface>
<!-- }}} -->
&reference.sem.setup;
&reference.sem.constants;
&reference.sem.reference;
</book>
<!-- Keep this comment at the end of the file
Local variables:
mode: sgml
sgml-omittag:t
sgml-shorttag:t
sgml-minimize-attributes:nil
sgml-always-quote-attributes:t
sgml-indent-step:1
sgml-indent-data:t
indent-tabs-mode:nil
sgml-parent-document:nil
sgml-default-dtd-file:"../../../manual.ced"
sgml-exposed-tags:nil
sgml-local-catalogs:nil
sgml-local-ecat-files:nil
End:
vim600: syn=xml fen fdm=syntax fdl=2 si
vim: et tw=78 syn=sgml
vi: ts=1 sw=1
-->
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