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>Semaphore, Shared Memory and IPC Functions</TITLE
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>XCI. Semaphore, Shared Memory and IPC Functions</H1
><DIV
CLASS="PARTINTRO"
><A
NAME="AEN82240"
></A
><DIV
CLASS="section"
><H1
CLASS="section"
><A
NAME="sem.intro"
></A
>Introduction</H1
><P
> This module provides wrappers for the System V IPC family of functions.
It includes semaphores, shared memory and inter-process messaging (IPC).
</P
><P
> 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.
</P
><P
> 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.
<DIV
CLASS="table"
><A
NAME="AEN82246"
></A
><P
><B
>Table 1. Limits of Shared Memory by the Unix OS</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><TBODY
><TR
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>SHMMAX</TD
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>max size of shared memory, normally 131072 bytes</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>SHMMIN</TD
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>minimum size of shared memory, normally 1 byte</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>SHMMNI</TD
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
> max amount of shared memory segments on a system,
normally 100
</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>SHMSEG</TD
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
> max amount of shared memory segments per process, normally 6
</TD
></TR
></TBODY
></TABLE
></DIV
>
</P
><P
> 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.
</P
><DIV
CLASS="note"
><BLOCKQUOTE
CLASS="note"
><P
><B
>Note: </B
>This extension is not
available on Windows platforms.</P
></BLOCKQUOTE
></DIV
></DIV
><DIV
CLASS="section"
><H1
CLASS="section"
><A
NAME="sem.requirements"
></A
>Requirements</H1
><P
>No external libraries are needed to build this extension.</P
></DIV
><DIV
CLASS="section"
><H1
CLASS="section"
><A
NAME="sem.installation"
></A
>Installation</H1
><P
> Support for this functions are not enabled by default.
To enable System V semaphore support compile PHP with the option
<TT
CLASS="option"
>--enable-sysvsem</TT
>.
To enable the System V shared memory support compile PHP with the option
<TT
CLASS="option"
>--enable-sysvshm</TT
>.
To enable the System V messages support compile PHP with the option
<TT
CLASS="option"
>--enable-sysvmsg</TT
>.
</P
></DIV
><DIV
CLASS="section"
><H1
CLASS="section"
><A
NAME="sem.configuration"
></A
>Runtime Configuration</H1
><P
> The behaviour of these functions is affected by settings in <TT
CLASS="filename"
>php.ini</TT
>.
</P
><P
> <DIV
CLASS="table"
><A
NAME="AEN82279"
></A
><P
><B
>Table 2. Semaphore Configuration Options</B
></P
><TABLE
BORDER="1"
CLASS="CALSTABLE"
><THEAD
><TR
><TH
ALIGN="LEFT"
VALIGN="MIDDLE"
>Name</TH
><TH
ALIGN="LEFT"
VALIGN="MIDDLE"
>Default</TH
><TH
ALIGN="LEFT"
VALIGN="MIDDLE"
>Changeable</TH
></TR
></THEAD
><TBODY
><TR
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>sysvmsg.value</TD
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>"42"</TD
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>PHP_INI_ALL</TD
></TR
><TR
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>sysvmsg.string</TD
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>"foobar"</TD
><TD
ALIGN="LEFT"
VALIGN="MIDDLE"
>PHP_INI_ALL</TD
></TR
></TBODY
></TABLE
></DIV
>
For further details and definition of the PHP_INI_* constants see
<A
HREF="function.ini-set.html"
><B
CLASS="function"
>ini_set()</B
></A
>.
</P
></DIV
><DIV
CLASS="section"
><H1
CLASS="section"
><A
NAME="sem.resources"
></A
>Resource Types</H1
><P
>
</P
></DIV
><DIV
CLASS="section"
><H1
CLASS="section"
><A
NAME="sem.constants"
></A
>Predefined Constants</H1
><P
>This extension has no constants defined.</P
></DIV
></DIV
><DIV
CLASS="TOC"
><DL
><DT
><B
>Table of Contents</B
></DT
><DT
><A
HREF="function.ftok.html"
>ftok</A
> --
Convert a pathname and a project identifier to a System V IPC key
</DT
><DT
><A
HREF="function.msg-get-queue.html"
>msg_get_queue</A
> --
Create or attach to a message queue
</DT
><DT
><A
HREF="function.msg-receive.html"
>msg_receive</A
> --
Receive a message from a message queue
</DT
><DT
><A
HREF="function.msg-remove-queue.html"
>msg_remove_queue</A
> --
Destroy a message queue
</DT
><DT
><A
HREF="function.msg-send.html"
>msg_send</A
> --
Send a message to a message queue
</DT
><DT
><A
HREF="function.msg-set-queue.html"
>msg_set_queue</A
> --
Set information in the message queue data structure
</DT
><DT
><A
HREF="function.msg-stat-queue.html"
>msg_stat_queue</A
> --
Returns information from the message queue data structure
</DT
><DT
><A
HREF="function.sem-acquire.html"
>sem_acquire</A
> -- Acquire a semaphore</DT
><DT
><A
HREF="function.sem-get.html"
>sem_get</A
> -- Get a semaphore id</DT
><DT
><A
HREF="function.sem-release.html"
>sem_release</A
> -- Release a semaphore</DT
><DT
><A
HREF="function.sem-remove.html"
>sem_remove</A
> -- Remove a semaphore</DT
><DT
><A
HREF="function.shm-attach.html"
>shm_attach</A
> -- Creates or open a shared memory segment</DT
><DT
><A
HREF="function.shm-detach.html"
>shm_detach</A
> -- Disconnects from shared memory segment</DT
><DT
><A
HREF="function.shm-get-var.html"
>shm_get_var</A
> -- Returns a variable from shared memory</DT
><DT
><A
HREF="function.shm-put-var.html"
>shm_put_var</A
> -- Inserts or updates a variable in shared
memory</DT
><DT
><A
HREF="function.shm-remove-var.html"
>shm_remove_var</A
> -- Removes a variable from shared memory
</DT
><DT
><A
HREF="function.shm-remove.html"
>shm_remove</A
> -- Removes shared memory from Unix systems</DT
></DL
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